RU2211527C2 - Electrical machine field suppression device - Google Patents

Abstract

FIELD: electrical engineering. SUBSTANCE: device used for magnetic field discharge in power switching apparatuses carrying inductive loads has nonlinear component, capacitive component, and two parallel-connected switching components, as well as voltage sensor connected in parallel with first switching component and current sensor whose output is connected to input of control unit. EFFECT: enhanced reliability of device; reduced time taken for field suppression. 1 cl, 1 dwg

Description

 The invention relates to electrical engineering, in particular to devices for damping the magnetic field of electric machines during short circuits (inside the machine) of the armature winding and external short circuits close to its conclusions, and can be used to evacuate a magnetic field in power switching devices with inductive loads.

 A device [1] is known for damping the magnetic field of synchronous electric machines, comprising a direct current circuit breaker included in the field winding circuit and a discharge circuit consisting of a series connection of two counter-parallel connected thyristors and a nonlinear discharge resistance connected in parallel with the field winding. When a field blank command is issued, the power contacts of the DC circuit breaker break the excitation current generated by the exciter, and the block contacts supply the main trigger pulse to the discharge thyristor. A backup pulse to the discharge thyristor is created from an increase in the excitation winding voltage, which occurs when the excitation current is cut off by the DC switch or when faults occur in the excitation circuits. When the discharge thyristor is turned on, a non-linear discharge resistance is connected in parallel with the excitation winding, on which the energy of the excitation winding is dissipated.

 The main disadvantage of this device is that the rotor current begins to break the DC switch, and the non-linear resistance comes into operation only after the voltage at the contacts of the switch reaches the voltage limit non-linear resistance. In the case of the use of conventional DC machines, due to the low voltage at their contacts when the current is cut off, the use of nonlinear resistances with a low voltage limitation, which reduces the rate of field suppression.

 To ensure quick field blanking, it is necessary to create a special switching device, at the contacts of which, when the current is interrupted, a sufficiently high voltage appears, which is necessary for the nonlinear resistances to enter into operation with a high level of limited voltage.

 A device for damping a field is also known, comprising a thyristor connected in series with an excitation winding, and a non-linear element through a second thyristor connected in parallel with the first thyristor. In parallel to the nonlinear element, a capacitive element is connected, the input of the control unit is connected to the short circuit sensor of the rotor, and the outputs of the control unit are connected to the control electrodes of the thyristors [2].

 A disadvantage of the known device is that it can reliably work only with electric machines of low power, since at high currents of the field windings of large electric machines in the first thyristor, due to a direct voltage drop, a significant power of losses is released on it, which heats this thyristor above the maximum permissible temperature pn transition.

 The invention is aimed at creating a high-speed field damping device that operates in a wide range of currents from units to ten thousand amperes and has increased reliability.

 The essence of the invention is to suppress the field of an electric machine using a device containing a non-linear element that limits the magnitude of the voltage on the field winding, which can be used as a varistor. For this, in addition to a non-linear element, the device contains two switching elements, a control unit whose outputs are connected to the control input of these switching elements, a capacitive element and a current sensor, the output of which is connected to the input of the control unit and an additional voltage sensor is inserted into it, the output of which is connected with an additional input of the control unit. The sensors are included as follows: a current sensor in series with the first switching element, and a voltage sensor in parallel with it. The non-linear element is installed parallel to the second switching element, and the capacitive element containing the capacitor and the charge unit is connected to the control electrode of the lockable thyristor, the series connection of which with the field-effect transistor forms the second switching element. Moreover, a switch is used as the first switching element.

 The advantage of the proposed device in comparison with the field damping devices used by ABB [1] is that the field damping is non-contact, because the first switching element is switched off without current due to the fact that the current of the field winding is intercepted by the opened thyristor. Such operating conditions of the switching element allow the use of serial DC switches used in the drive. This circumstance significantly reduces the cost of the switching element, since circuit breakers with a main and arcing contact are made by a narrow sector of manufacturers and are very expensive. Since in the proposed device the EMF necessary to turn on the varistors is created by quickly turning off the thyristor when the contacts of switch 1 are fully open, there is no need to turn on its current power contacts in series.

The drawing shows a diagram of a device for damping the field of an electric machine, where:
1 - switch;
2 - current sensor;
3 - field winding;
4 - 2nd switching element;
5 - lockable thyristor;
6 - field effect transistor;
7 - non-linear element;
8 - capacitor;
9 - charge unit;
10 - voltage sensor;
11 - control unit;
12 - coil trip switch;
13 - capacitive element;
14 - power supply to the field winding.

 The device operates as follows.

 To excite the electric machine, the first switching element (switch 1) is turned on and connects the excitation winding 3 to the power source of the excitation winding 14. A current flows through the excitation winding.

 By the command to turn off the field damping device that enters the control unit 11, the latter simultaneously gives signals to the inputs of the switching elements: for the first, the trip coil 12, and for the second, the gate of the field effect transistor 6. Due to the higher speed compared to the switch, the field effect transistor 6 opens faster than the contacts of switch 1 have time to open. A current from the charge unit 9 starts flowing through the control electrode of the lockable thyristor 5, and the second switching element 4 opens, bypassing the first switching element (switch 1). Thus, when the contacts of the first switching element (switch 1) are opened, the current in the field circuit of the field winding will go to the previously opened second switching element 4 (thyristor 5, field effect transistor 6). At the point in time when the current flowing through the first switching element drops to zero, which is detected by the control unit 11 using the current sensor 2, the control unit will turn off the field effect transistor 6. In this case, the field current of the field winding through the anode - control electrode of the lockable thyristor 5 will start charge the capacitor 8 of the capacitive element 13.

 When the current of the control electrode of the lockable thyristor 5 reaches the threshold necessary for locking the thyristor, it will turn off and the stored energy in the field coil will be released in non-linear element 7 (varistor), i.e. the process of quenching the field of an electric machine will occur.

 In the case of spontaneous shutdown of the first switching element (switch 1), voltage begins to increase at its contacts as a result of the action of the self-induction EMF of the field winding. This voltage is measured by the voltage sensor 10 and when it exceeds the threshold determined by the control unit 11, the latter, acting on the control input of the second switching element 4, opens it. A current flows through the control electrode of the lockable thyristor 5. Further, the process proceeds in the same way as in the first case.

Sources of information
1. Hansjorg Herzog and Taborda ABB Industrie AG, Turgi / Switzerland "Important design features of modem static excitation systems"'95 Three Gorges Project Technology: International Seminar, Yichang.

 2. Copyright certificate of the USSR 1588428, Cl. H 02 P 9/12, 1975 (prototype).

Claims (1)

 A device for damping the field of an electric machine, containing a nonlinear element, a capacitive element consisting of a capacitor with a charge unit and two parallel-connected switching elements, the control inputs of which are connected to the outputs of the control unit, the input of which is connected to the output of the current sensor, characterized in that additionally a voltage sensor is introduced, the output of which is connected to an additional input of the control unit, the voltage sensor is connected in parallel with the first switching element, and the current sensor is tion with it, a nonlinear element connected in parallel with the second switching element, second switching element is comprised of serially connected field effect transistor and a gate turn-off thyristor and a capacitive element connected to the control electrode of the thyristor and as a first switching element used in the switch.