Patent GB-1320703-A (GB)
Title: System for computing electric power flow
IPC: G06G7/63
Filed: 1970-07-07
Abstract: 1320703 Computing power in electrical systems TOKYO DENRYOKU KK and MITSUBISHI DENKI KK 7 July 1970 32 829/70 Heading G4G Analogue apparatus for computing power flow in an electric power system, comprises a resistance network having branches simulating branch lines of the system, and generators and loads simulating the corresponding elements of the system, the simulation proceeding according to the following principles described with reference to a typical system branch (Fig. 1a) and a typical network branch (Fig. 1b). The power flowing in the system branch is assumed to be:- where P mn  is the active power, Q mn  the reactive power, V m  the complex voltage at m, and I* the conjugate of the complex current in Z mn . The R.H.S. of this expression is expanded in terms of trigonometrical functions, and simplified using well-known approximations. Further it is assumed that (1) the active power P mn  is determined only by the phase differences between the voltages V m  and V n , and (2) the reactive power Q mn  is determined only by the difference in voltage between the nodes m and n (see equations (5), (6), not given here). These simplifications result from the assumptions that V m #V n  and that R mn  is negligibly small compared with X mn . We have:- where it is assumed that the voltages V m  and V n  differ from unit voltage by #V m  and #V n . For the resistive branch in the simulating network (Fig. 1b) we have:- In the simulating network, D.C. constantvoltage sources correspond to generators for which Vg is known; D.C. constant-current sources correspond to generators for which Qg is known; and D.C. constant-voltage or constantcurrent sources corresponding to the loads, these sources being of such polarity as to correspond to power dissipation instead of generation. The D.C. sources are connected between the nodes of the network and earth (Figs. 4, 5, not shown). These are two distinct modes of use:- (a) computation of reactive power and voltage relative to bus-bar voltage; or (b) computation of active power and phase angle relative to phase angle of a reference bus-bar. In the first case, the reactive power of each load and the known reactive power or voltage of each generator are set by adjustment of the D.C. sources. Currents measured in the simulating network then correspond to the reactive power at corresponding points in the system, and voltages measured to system voltages. In the second case, a reference point in the network is earthed to correspond to the bus-bar and the D.C. sources are set to correspond to the active power of each system load and generator. Currents measured correspond to active power and voltages measured to phase angles. Fig. 5 shows a simulated generator unit comprising three potentiometers 14P, 14Q, 14V fed from the same source 10 and connected by a system of switches and relays 16, 18, 20, 22, 24, 34 to two inverting operational amplifiers 28, 36. During setting for computation of P and #, the relays and switches are set such that a constantcurrent circuit is formed by the closed loop comprising amplifier 28, resistor 30 and inverter 36, the output being proportional to the setting of potentiometer 14P. For computing Q and V, the relay 16 is actuated to connect terminals 16a, 16c together and the switch 18 actuated to connect 18a either to 18b or 18c to obtain either a constant current proportional to the setting of potentiometer 14Q or a voltage proportional to the setting of potentiometer 14V. The potentiometer 14Q is centre-tapped so that negative currents corresponding to negative Q may be obtained. When switch 18 is changed over to connect contacts 18a and 18c, contacts 20, and 22a are closed, and relays 24, 34 are operated to remove resistance 30 and inverter 36 from the closed loop. The setting of potentiometer 14V then determines a constant-voltage output of either sign from the amplifier 28. A similar circuit is described for simulating system loads (Fig. 3, not shown).