Abstract
Content
- 1. Features of protection of synchronous motors
- 2. Differential motor protection
- 3. Power Loss Protection (PLP)
- 4. Asynchronous protection
- References
1. Features of protection of synchronous motors
During start-up, the synchronous electric motor draws an increased current from the mains, which damps as the slip decreases, just like an asynchronous electric motor. To reduce undervoltage and inrush currents, powerful synchronous electric motors are started through a reactor, which is then shunted. The protection of synchronous electric motors, as well as the RE of asynchronous electric motors, must be disconnected from the currents that occur when they are started or self-starting, which occurs when the voltage is restored in the network.
The timing of a synchronous motor depends on the mains voltage.
Emergency automation (EA) – a set of devices that provides measurement and processing of parameters of the electric power regime of the power system, the transfer of information and control commands and the implementation of control actions in accordance with the specified algorithms and settings to identify, prevent the development and eliminate emergency mode of the power system.
2. Differential motor protection
This is a quick protection for high power motors against phase to phase short circuits. Usually consists of two degrees – differential cutoff (DTO) and diff. protection with braking (DZT). The latter can be selected with a trip setting lower or higher than the rated motor current.
3. Power Loss Protection (PLP)
Protection against power loss turns off the engine after it enters the generator mode, i.e. when the power at the installation begins to flow from the engine to the network. This direction of power means short circuit or disconnection of equipment in a higher network.
To determine the generator mode, the power direction algorithm is used (currents through the stator and bus voltage).
PLP can turn off the engine to provide self-starting more responsible. In principle, this protection can also be used on HELL, as well as group on the bus section (current through the input). In addition, a launching body, similar to the PLP, is used in high-speed automatic transmissions (BAVR), which are now actively introduced in the networks of industrial enterprises.
4. Asynchronous protection
Asynchronous protection shuts off the synchronous motor in case of loss of excitation. In addition, a simple or combined (with preliminary unloading) LED resynchronization may be provided to restore normal operation parameters.
In case of synchronism violation, the frequency of rotation of the electric motor decreases, and it goes into asynchronous mode. At the same time, currents appear in the starting winding and the rotor circuit, creating an additional asynchronous moment, under the influence of which the synchronous motor can remain in operation with some slip.
References
- Чернобровов Н. Н., Семенов В. А.
Релейная защита энергетических систем
, 1998 г., стр. 715, рис. 19.12. - Шабад М. А.
Релейная защита на электроподстанциях, питающих синхронные электродвигатели
, Библиотека электромонтера, вып. 565 Л.: Энергоатомиздат, 1984 г., стр.53–54, рис. 19. - Шабанов В. А., Алексеев В. Ю. Патент № 2342755, Устройство защиты от потери питания / Опубликован 27.12.2008. Бюл. № 38.