Abstract: The invention relates to a method for managing an electrical network. The electrical network includes two power centers making it possible for each one to supply several loads, each power center including: an electrical power supply bus, a plurality of reversible converters making it possible to exchange energy between the bus and the various loads , routing means making it possible to vary an association between the converters and the loads, an energy storage element. According to the invention, if for a first of the power centers, the regenerated power cannot be dissipated in the other loads associated with the first center, the regenerative load dissipates its power toward the bus of the second power center.

Abstract: A method and apparatus for power wiring. In one embodiment, the apparatus comprises a splice box comprising (i) a plug having a plurality of plug pins, each plug pin of the plurality of plug pins for coupling to a conductor within a cable adapted for coupling to a power line; (ii) a first pin receptacle for coupling to a first guide pin of a connector; and (iii) a first pair of retention bars disposed within the first pin receptacle, the first pair of retention bars for retaining the first guide pin.

Abstract: A wind turbine generator park (1) for supplying power to a power system (37), the park having an assigned first droop response characteristic for use in responding to an under-frequency occurrence on the power system (37). The park comprises a first comparator (108) for generating a first signal when the park is operating according to a curtailed condition, a second comparator (100) for indicating that a change in a frequency of a voltage or current on the power system (37) is greater than a first threshold value, and a controller (114) responsive to the first and second signals for controlling the park according to a second response characteristic causing the park (1) to supply an amount of power to the power system (37) greater than the power supplied according to the first droop response characteristic.

Abstract: A vehicle powering wireless receiver for use with a first electromagnetic resonator coupled to a power supply. The wireless receiver includes a load configured to power the drive system of a vehicle using electrical power, and a second electromagnetic resonator adapted to be housed upon the vehicle and configured to be coupled to the load, wherein the second electromagnetic resonator is configured to be wirelessly coupled to the first electromagnetic resonator to provide resonant, non-radiative wireless power to the second electromagnetic resonator from the first electromagnetic resonator; and wherein the field of at least one of the first electromagnetic resonator and the second electromagnetic resonator is shaped using a conducting surface to avoid a loss-inducing object.

Abstract: The present invention relates a wind turbine generator with an electrical generator, a dump load unit, for dissipating power, a wind turbine power controller and a damping controller both arranged to control wind turbine components based on a damping reference signal, the damping reference signal is a combined signal, and comprises a first reference signal and a second reference signal, the second reference signal is an oscillating part, the wind turbine power controller is controlling the power from the electrical generator according to the first reference signal and the damping controller is controlling the dump load unit to dissipate power according to the second reference signal. The invention also relates to a method for damping oscillations with wind turbine generators.

Abstract: An object of the invention is to make the charging power as high as possible in a battery charging control system for selectively charging a plurality of batteries having different voltages with energy generated by an alternator. To achieve the object, the battery charging control system according to the invention includes an alternator having a variable generation voltage and a plurality of batteries having different charging voltages, wherein maximum generation power defined as the highest power that the alternator can generate and maximum charging power defined as the highest power that each battery can accept are obtained, and a battery for which the charging power is highest is selected to be charged based on a comparison of the maximum generation power and the maximum charging power.

Abstract: A photovoltaic (PV)-based AC module (module) includes a PV panel and a three-phase micro-inverter system attached to or integrated directly into the PV panel including a DC/AC inverter stage including first, second and third phase circuitry each having a plurality of semiconductor power switches. A first, second and third control input driver are coupled to drive control inputs of the plurality of semiconductor power switches in the first, second and third phase circuitry, respectively. The module can include a control unit coupled to drive the first, second and third control input driver, and a transceiver and antenna coupled to the control unit for implementing wireless communications.

Abstract: A voltage regulator circuit for providing a regulated output voltage is provided. The voltage regulator circuit includes an error amplifier configured to provide a control signal based on at least a portion of a fed-back output voltage and a reference voltage. A first output stage is configured to operate at a first supply voltage and provide the regulated output voltage based on the control signal. At least one second output stage configured to operate at a second supply voltage different from the first supply voltage and provide the regulated output voltage based on the control signal. A switch-over unit is configured to switch over the control signal between the first output stage and the second output stage.

Abstract: Disclosed herein is a power feeding apparatus, including: a power feeding portion adapted to feed an electric power in a wireless manner; and a storage body storing therein the power feeding portion. The storage body includes a main body, a first storage portion formed within the main body and storing therein the power feeding portion, and at least one second storage portion formed so as to be adapted to store or retrieve a power receiving apparatus as a storage object in or from the main body, the electric power of the power feeding portion stored in the first storage portion being adapted to be fed from the at least one second storage portion. At least a magnetically shielding portion is formed in an outer peripheral portion, and the at least one second storage portion forms a magnetically closed space in a state of being stored in the main body.

Abstract: A method of controlling a plurality of gensets during a failsafe condition is provided. The method may include operating one or more of the gensets according to a modified isochronous control scheme, and operating a remainder of the gensets according an adaptive droop control scheme. The modified isochronous control scheme may include varying the frequency of each isochronous genset with respect to load for lower-range loads and upper-range loads, and maintaining the frequency of each isochronous genset at nominal frequencies for mid-range loads. The adaptive droop control scheme may include adjusting the frequency of each droop genset to match the frequency of the isochronous gensets, and varying the load of each droop genset with respect to frequency for lower-range loads and upper-range loads.

Abstract: A system for producing and distributing electrical energy over an electrical network of a geographic area, includes a first entity for generating electrical energy, which operates in a steady state and generates at least a portion of the electrical energy; a second entity for intermittently generating the electrical energy from renewable energy; a third entity, which is capable of operating in a load-following state, the system being sized such that the profile of the change in total energy potential of the geographic area over the span of one year, corresponding to the sum of the profile of the change in the amount of electrical energy distributed by the main entity and the profile of the change in the amount of electrical energy generated by the second entity over the span of one year, is less than the profile of the change in the demand for electrical energy of the network.

Abstract: A breaker 162 is opened when a pantograph 101 is lowered. The pantograph 101 is connected to an overhead wire 200. Voltage and its phase of the overhead wire are detected by a detector 161. Power is supplied from a power storage device 150c to a tertiary winding 112c via a power converter 14c such that a primary side of the main transformer 110 has the same voltage and phase as the overhead wire so as to reversely excite the main transformer 110. When the voltage of the main transformer 110 has the same phase as the voltage of the overhead wire 200, the breaker 162 is turned on and then the pantograph 101 is raised, to connect the overhead wire 200 and the main transformer 110 to each other, thereby preventing the occurrence of an excitation inrush current to the main transformer 110.

Abstract: A power distribution system comprising a point of common connection that receives electric power supplied by a first power generation system and a second generation system, with the second power generation system that comprises a renewable electric power generator; a transmission line operatively connected to the point of common connection for conducting the electric power between the point of common connection and an external AC electric network. The power distribution furthermore comprises a capacitive compensator connected in series with the transmission line to compensate for a reactive power component of the electric power conducted by the transmission line; and a shunt arranged flexible AC transmission system that mitigates a sub-synchronous resonance effect caused at least in part by the capacitive compensator. A flexible AC transmission system controller of the flexible AC transmission system comprises a damping effect on sub-synchronous oscillations included in the sub-synchronous resonance.

Abstract: It is an object of the present invention to suppress such a situation that electric power selling becomes impossible while the deterioration of supply power is prevented. The electric power selling system of the present invention comprises a solar battery 3 as a power generator, and a control unit 7 which is connected with the solar battery 3 and a distribution line and configured to convert output voltage of the solar battery 3 into variable voltage for electric power selling. The electric power selling system further comprises a transmitter 60 connected with the distribution line, said transmitter 60 being configured to measure voltage of the distribution line and to supply the control unit 7 with an instruction value obtained based on the measured voltage value. The control unit 7 is configured to convert the output voltage of the solar battery 3 into the voltage for electric power selling based on the instruction value.

Abstract: The invention relates to a method for damping grid oscillations. The oscillations may be damped by controlling e.g. wind turbine generators to inject power to the grid in anti-phase with the grid oscillations. Instead of controlling one or more wind turbine generators to generate the same anti-phase power signal, a plurality of wind turbine generators are controlled so that each of them only generates a part of the anti-phase power signal, but so that all of the wind turbine generators in combination generates the entire anti-phase power signal.

Abstract: The present invention concerns a method of feeding electric power into an electric network wherein the feed is effected by means of at least one wind power installation with a first feed-in arrangement at a feed-in point into the electric network, and the feed is effected in dependence on electric parameters in the network and measurement values of the electric parameters or measurement values for determining the electric parameters are detected at measurement times at predetermined time intervals and wherein the measurement times are synchronized to an external time signal available outside the first feed-in arrangement.

Abstract: A power system for data center, which comprises: a critical electrical equipment, an alternating current (AC) transformer, an AC power distribution unit (PDU), a rectifier transformer, and a DC PDU. The critical electrical equipment is disposed in the data center. The AC transformer is utilized to receive a first high AC electrical power from a first power utility and transform it to a low AC electrical power, and the AC PDU receives the low AC electrical power and applies the low AC electrical power to the critical electrical equipment of the data center. Further, the rectifier transformer is utilized to receive a second high AC electrical power from a second power utility and transform and rectify it to a low direct current (DC) electrical power, and a DC PDU receives the low DC electrical power and applies the low DC electrical power to the critical electrical equipment.

Abstract: A plurality of generators can be connected in parallel to a common electrical bus. Each generator has a controller that regulates the voltage and frequency of the electricity being produced. Before a given generator connects to the electrical bus, its controller senses whether electricity is present on the bus and if not, the connection is made. Otherwise, the controller synchronizes the electricity being produced to the electricity is present on the bus before the connection occurs. The controller in each generator may also implement a load sharing function which ensures that the plurality of generators equitably share in providing the total amount of power demanded by the loads. The load sharing can be accomplished by controlling the generators to operate a substantially identical percentages of their individual maximum power generation capacity.

Abstract: An energy harvesting apparatus includes: a capacitor configured to store energy generated by an energy harvesting element; and a switch connected to the capacitor and configured to switch energy supply from the capacitor to a load based on a capacitor voltage with which the capacitor is charged. An energy harvesting system includes: energy harvesting elements; energy harvesting apparatuses which are provided to respectively correspond to the energy harvesting elements; and a load as an energy supply destination connected to the energy harvesting apparatuses.

Abstract: Disclosed herein is a method for generating an injected current of a fuel cell stack performed in an apparatus for generating an injected current of a fuel cell stack, the method including: extracting a first frequency current and a second frequency current by passing alternating currents of different frequencies through a plurality of filters, respectively; generating a summed frequency current by summing the first frequency current and the second frequency current; and applying the summed frequency current to the fuel cell stack. Therefore, it is possible to operate the fuel cell stack by applying the summed current obtained by summing the alternating current for calculating the total harmonic distortion (THD) and the alternating current for calculating the impedance to the fuel cell stack.

Abstract: A circuit and method for allocating power among two or more generators to a single load on a shared bus includes a sharing regulator and a feedback loop for each generator. A digital share command input and current in the feedback loops will cause the sharing regulators to alter the power of the generators at the generator outputs, thereby allocating the load on the shared bus according to the share command, and confirming the allocation of power at the outputs.

Abstract: A parallel operation control method for different type power generation apparatuses to shift the power generation apparatuses having respective different drooping characteristics, in which the drooping characteristic is defined as a characteristic of decrease of a rated frequency along with an increase of a load, from independent operation of the power generation apparatuses under suitable drooping characteristics to parallel operation thereof to drive a common drive target, includes determining a load of one of the power generation apparatuses by subtracting a load of the other of the power generation apparatuses from a predetermined required load; changing a drooping characteristic of the one of the power generation apparatuses so as to coincide with a drooping characteristic of the other of the power generation apparatuses; and controlling the one of the power generation apparatuses so as to maintain frequency at the time of changing the drooping characteristic.

Abstract: A bulk energy storage device for an energy source. The energy storage device includes a circular or conveyor, such as a rail track, which may be formed with slopes. An electrical conductor, such as a third rail or overhead electric cable, connects to an electric grid. Coupled masses, such as rail cars, which travel on the conveyor, have motor/generators that are electrically connected to the conductor. The coupled masses can be raised on a magnetic field and driven by a linear electric motor having a stator embedded in the track and a rotor attached to the undersurface of the masses. Power from the grid is drawn via the third rail to propel and store energy in the ring of masses. When the grid needs to draw power from storage, the linear motor acts as a generator, supplying power to the grid by converting mass momentum into electric power.

Abstract: The dynamic system is part of a dynamic apparatus having at least one photovoltaic generator, at least one battery and at least one device for controlling the dynamic apparatus. The method for controlling the dynamic system on the basis of sunlight involves electrically isolating the photovoltaic generator from the battery, reading the no-load voltage of the photovoltaic generator, determining a numerical value on the basis of the no load voltage, corresponding to the no-load voltage reading, and comparing the predetermined numerical value with at least one reference threshold value. When the predetermined numerical value corresponds to a value range limited by at least one such reference threshold value the dynamic system is controlled so as to thereon confer a configuration corresponding to the value range.

Abstract: Vehicles, systems, and methods are disclosed for providing and directing first power, such as vehicle generator power, and alternate sources of power. In a particular embodiment, a vehicle includes a power distribution grid that includes a plurality of power sources and a plurality of distributions buses configured to distribute power from the plurality of power sources. The plurality of power sources include an engine-driven power source is configured to provide first power where the first power has first power characteristics. The plurality of power sources also includes a plurality of engine-independent power sources including a first alternate power source configured to provide first alternate power. The first alternate power has first alternate power characteristics that are different than the first power characteristics. The plurality of engine-independent power sources also includes a second alternate power source configured to provide second alternate power.

Abstract: A control system for use with a genset is disclosed. The control system may have a bus configured to receive power from the generator set, and a first sensor configured to generate a first signal indicative of a characteristic of power on the bus. The control system may also have a second sensor configured to generate a second signal indicative of an engine parameter of the generator set, and a controller in communication with the first and second sensors. The controller may be configured to synchronize an electrical output of the generator set with the power on the bus based on the first and second signals.

Abstract: A DC/AC converter for converting DC power of a number of inductively connected generators into power grid conformal AC power for feeding into a connected power grid with a number of phases, includes an intermediate circuit with a positive and a negative intermediate circuit connection, and for each phase, a bridge. Each bridge includes a first switch between the positive intermediate circuit connection and a phase terminal, a second switch connected between a positive generator terminal of the generator and the phase terminal, a third switch connected between a negative generator terminal of the generator and the phase terminal, and a fourth switch between the negative intermediate circuit connection and the phase terminal.

Abstract: A maximum power point tracking (MPPT) device is provided that includes a converter, having a switched mode topology, where the switched mode topology includes a boost topology that establishes a variable transfer ratio between a variable input voltage and a variable output voltage of the converter, where the switched mode topology changes according to a power load on a power generator. The MPPT device further includes a control section, where the control section maximizes an output power of the power generator by controlling the variable transfer ratio, where the MPPT device optimizes an electrical operating point, of the power generator.

Abstract: An information processing apparatus includes: a plurality of electric power generating elements; detection means for determining whether each of the plurality of electric power generating elements has an electromotive force equal to or higher than a predetermined value; determination means determining an input operation performed by a user by identifying an electric power generating element having an electromotive force below the predetermined value when at least one of the plurality of electric power generating elements is determined as having an electromotive force below the predetermined value according to the detection means; processing means carrying out a process associate with the input operation determined by the determination means; and bypass means which is provided in parallel with the electric power generating elements and through which a current flows when the electric power generating elements have an electromotive force below the predetermined value.

Abstract: Systems and methods for a mobile power conditioning platform are disclosed. According to one embodiment of the invention, a mobile power conditioning platform is positioned proximate to a power grid, coupled to the power grid via an offboard power coupling, coupled to an onboard electrical system of a vehicle via a vehicle power coupling, and transfers electric power between the power grid and the onboard electrical system. One or more onboard generators of the vehicle may modify operation at least partly in response to the transfer of electric power.

Abstract: A power distribution system is described that does not rely on a fixed frequency and which therefore allows prime movers to run at different speeds in response to load demand, typically so that fuel consumption and/or harmful exhaust emissions is/are minimised. A marine power distribution and propulsion system can include an ac busbar adapted to carry a variable-frequency ac distribution voltage. A plurality of ac generators are connected to the busbar, each having an associated prime mover such as a diesel engine, turbine etc. A power management controller is adapted to vary the rotational speed of the prime movers with reference to the electrical load on the ac busbar such that the generators provide a variable frequency output during normal operation of the power distribution system. Such operation is to be contrasted with conventional distribution systems which have a fixed frequency.

Abstract: Methods and apparatus are provided for using a renewable source of energy such as solar, wind, or geothermal energy. In some embodiments, the method may include generating electric energy from a renewable form of energy at a plurality of locations at which reside an electric power line associated with an electric power grid. The electric energy generated at each location may be transferred to the electric power line to thereby supply electric energy to the electric power grid.

Abstract: A system designed to optimize fuel efficiency of a power grid includes a set of controllable generators designed to supply power to the power grid. Each generator in the set is associated with a controller, a set of loads designed to draw power from the power grid, and a grid controller designed to provide a load partitioned configuration for the set of controllable generators, based at least partly on the power draw of the set of loads.

Abstract: The inventions relates to a system for conditioning of power from a turbine, the turbine comprising at least one turbine blade (1) connected to a rotating hub (2), the rotating hub (2) is arranged to drive a generator (5). The generator is a multi pole synchronous generator (5) connected via a plurality of galvanic isolated three-phase cables (11) to a multi level frequency converter (25), the generator (5) also being arranged to feed current to the frequency converter (25) through the three-phase cables (11). The multi level frequency converter (25) is constituted by a plurality of elements arranged in columns and coupled in cascading order to add inverted voltage.

Abstract: Three or more portable generators are linked for synchronized operation. Power cables link each generator to a linkage box which connects the power in parallel and connects an outlet thereto. Communication cables link a software module in each generator with the linkage box. The modules vary the generator operation to generate a voltage amplitude and phase matching that of the first generator that is connected to the box that begins power generation, so that all generators share the load equally until their power output limits are reached.

Abstract: Methods and apparatus are provided for using a renewable source of energy such as solar, wind, or geothermal energy. In some embodiments, the method may include generating electric energy from a renewable form of energy at a plurality of locations at which reside an electric power line associated with an electric power grid. The electric energy generated at each location may be transferred to the electric power line to thereby supply electric energy to the electric power grid.

Abstract: A method for controlling power generation equipment, including bringing a generator online into a shared power bus environment, is described. The method includes determining whether the shared power bus is currently active, and whether a voltage determination fault is present with respect to a specific generator. Where the shared power bus is inactive and no fault is present, the generator is brought online in response to a load request. Where the shared power bus is active, the generator is synchronized with the shared power bus before the generator is brought online.

Abstract: A PLC cable modem is provided which includes an analog electromagnetic field transducer for generating an electromagnetic field based on an analog electrical signal and also for generating an analog electrical signal based on an electromagnetic field. The PLC cable modem also includes an analog signal processing unit operatively coupled to the analog electromagnetic field transducer and a digital signal processing unit for processing signals received from (or to be sent to) the analog signal processing unit. An interface port is provided for communicating digital signals to and from a data transmission or receiving device.

Abstract: A system and method for supplying power to a variable speed motor for rotating a shaft may include generating an A/C output having a variable frequency corresponding to speed of a prime mover, where the speed of the prime mover is equal to or greater than a predetermined speed limit. The A/C output of the prime mover may be distributed to the variable speed motor such that the speed of the variable speed motor is varied relative to the frequency of the A/C output. The variable speed motor may be electrically disconnected from the A/C power when the speed of the prime mover being used to drive the variable speed motor is equal to or within a predetermined range of the predetermined speed limit. An alternate A/C output may be distributed to the variable speed motor after the A/C power is electrically disconnected from the variable speed motor.

Abstract: Systems and methods for state-based adjustment of power and frequency are described. A primary generator of a system includes a primary power supply for supplying a primary radio frequency (RF) signal to an electrode. The primary generator further includes an automatic frequency control (AFC) to provide a first frequency input to the primary power supply when a pulsed signal is in a first state. A secondary generator of the system includes a secondary power supply for supplying a secondary RF signal to the electrode. The secondary generator also includes an AFC to provide a second frequency input to the secondary power supply when the pulsed signal is in the first state. The secondary generator includes an AFC to provide a third frequency input to the secondary power supply when the pulsed signal is in a second state. The system includes a digital pulsing source for generating the pulsed signal.

Abstract: A reference generator with programmable m and b parameters and methods of use are provided. A circuit includes a first generator operable to generate a first voltage including a fraction of a supply voltage. The circuit further includes a second generator operable to generate a second voltage. The circuit further includes a mixer and buffer circuit operable to output a reference voltage including a sum of the first and second voltages.

Abstract: Operating a wind farm in which the power generated by the wind energy installations is fed to a power supply system via a system internal to the wind farm and via a substation is disclosed. The farm director of the wind farm can ascertain a standard target voltage value and transmit it to the control units of the individual wind energy installations on the wind farm, which can use an overall factor to regulate the reactive power generated by a wind energy installation. The overall factor can be calculated from the difference between the actual voltage across the wind energy installation and the target voltage value, multiplied by a gain factor. On account of the impedance in the internal system of the wind farm, wind energy installations situated far away from the substation thus generate less reactive power than the wind energy installations which are situated close to the substation.

Abstract: This electricity producing installation (1) includes electricity producing devices (14, 16, 18, 20) at least partly immersed in water, each electricity producing device comprising a rotary mechanical receiver and an alternator (22) comprising at least one rotor (23) and at least one stator (24), a rotor of the alternator being able to be set into rotation by the rotary mechanical receiver. Each electricity producing device (14, 16, 18, 20) produces an electric AC signal with variable voltage and frequency conveyed by an at least partly immersed electric transport cable (32, 36, 38, 40). The installation further comprises an interconnection device (34) to which are connected at the input in parallel electric transport cables (32, 36, 38, 40) and which provide at the output a joint electric signal (S?) with variable frequency and voltage, the current amplitude of which is equal to the sum of the input currents.

Abstract: A reactive power compensation method includes generating a variable power factor curve for at least one power generator based on information regarding network parameters; obtaining a value of an active output power parameter from the at least one generator; computing a reactive power based on the variable power factor curve and the value of the active power output parameter of the at least one generator; generating a reactive power compensation command based on the computed reactive power; and transmitting the reactive power compensation command to the at least one power generator for controlling operation of the at least one power generator.

Abstract: A power system for use in a power facility is disclosed. The power system may have a first generator set with a first engine drivingly coupled to a first generator, and a second generator set with a second engine drivingly coupled to a second generator. The power system may also have a common bus, and a controller in communication with the first and second generator sets. The controller may be configured to direct power from the first generator to the common bus, and synchronize a power output from the second generator with a power output from the first generator. The controller may be further configured to postpone power from the second generator being directed to the common bus until the first and second engines are substantially mechanically synchronized.

Abstract: A power supply device adapted for supplying electrical power to a load comprises a first electrical generator adapted for providing a first output current having a first phase angle; at least a second electrical generator adapted for providing a second output current having a second phase angle independent of the first phase angle; and a combination unit adapted for combining the first output current and the second output current to a combination current having reduced harmonics compared to the first and second output currents.

Abstract: A system parallels engine-generators on a common bus and includes circuit breakers and automatic voltage regulators. Each engine-generator includes an output having an alternating current voltage. Each breaker is between the output of a corresponding engine-generator and the bus. Each regulator includes a first mode controlling field excitation for a corresponding engine-generator and a second mode automatically controlling the AC voltage.

Abstract: A renewable power transmission overlay for generating electrical power of regional extent includes three types of generators for generating electrical power from wind, solar radiation and biomass, along with a plurality of region-wide transmission facilities with each region-wide transmission facility having at least one collection facility for collecting electric power from at least one of the generators for generating electrical power. Inter-regional transmission facilities are included which selectively couple the electric power generated by at least two of the types of electrical generators and at least one substation electrical facility is coupled to each of the collection facilities of the region-wide transmission facilities for downloading the electrical power generated to a local electrical transmission grid which, preferably, firms the electric power that is generated, transmitted and downloaded to the local electrical transmission grid.

Abstract: A control system is provided for use with a plurality of generator sets. The control system may have a bus, an arbitration relay, a switching device, a control module, and first, second, and third discrete signal cables. The control module may be configured to receive a group start signal and initiate startup of a first of the plurality of generator sets, and to generate a signal on the first discrete signal cable based on an operational status of the first of the plurality of generator sets. The control module may also be configured to determine if the second discrete signal cable is active, to activate the second discrete signal cable and the arbitration relay based on the determination, and to activate the switching device to connect the first of the plurality of generator sets to the bus based on a status of the third discrete signal cable.

Abstract: An electrical generator arrangement comprising a distribution network having a first generator and a second generator, the first generator arranged to provide electrical power to a transmitter source, the second generator coupled to the distribution network by a switch to enable isolation of the second generator, the switch associated with an electrical characteristic comparator to compare the phase and/or frequency of the voltage provided by the second generator with the incidental modulation of a transmitter signal from the transmitter due to variations in the phase and/or frequency of the voltage provided by the first generator to the transmitter, the comparator arranged to operate the switch to isolate or connect the second generator to the distribution network dependent upon a variation in the change of the phase and/or frequency of the voltage provided by the second generator and the incidental modulation of the transmitted signal.