ABB RELION REX640 Technical Manual page 1075

Protection and control

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1MRS759142 F

by a binary input, a horizontal communication input or an internal signal of

the protection relay's program. The influence of the BLOCK signal activation is

preselected with the global setting

mode, the operation timer is frozen to the prevailing value. In the "Block all" mode,

the whole function is blocked and the timers are reset. In the "Block OPERATE

output" mode, the function operates normally but the OPERATE output is not

Use of distributed power generating units ( PGU) is rapidly increasing due to

liberalized markets (deregulation) and the global trend to use more renewable

sources of energy. As the capacity of these generating units increase, they are

connected directly to medium voltage networks. Until recent years it had been a

practice by grid operators to disconnect the distributed power generator from the

network in case of fault in the network.

If there is a considerable loss in the power generation, it may affect the system's

ability to recover. To ensure power system stability, various grid codes have revised

their requirements and therefore require that the distributed PGUs have to make a

contribution to network support. In case of network faults, the distributed power

generator should not be immediately disconnected from the network. Instead, as a

matter of principle, generating plants connected to the medium-voltage network

must be capable of participating in steady-state voltage control and dynamic

network support. However, if the generators stay connected, it must be ensured

that they do not take reactive power from the network because this may lead

to collapse of the grid. DQPTUV is used for detecting such situations, that is,

simultaneous undervoltage and reactive power (under excited generators) and trip

the generators.

The protection function DQPTUV is developed considering various grid codes. For

example, in the BDEW Technical Guideline "Generating Plants Connected to the

Medium-Voltage Network" (June 2008 issue, Germany), it is stated that if all three

phase-to-phase voltages at the grid connection point decrease and remain at and

below a value of 85% of the rated and if reactive power is simultaneously consumed

at the grid connection point (under-excited operation), the generating facility must

be disconnected from the network with a time delay of 0.5 s.

Technical Manual

Blocking mode setting has three blocking methods. In the "Freeze timers"

Blocking mode .

Protection functions