ABB RELION REX640 Скачать руководство пользователя страница 882

Страница: 882 / 1960

be controlled 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

Blocking mode.

The

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

mode, the operation timer is frozen to the prevailing value, but the

OPERATE

output

is not deactivated when blocking is activated. 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 activated.

4.5.6.6

Application

PSPTUV can be applied for protecting a power station used for embedded

generation when network faults like short circuits or phase-to-earth faults in a

transmission or a distribution line cause a potentially dangerous situations for the

power station. A network fault can be dangerous for the power station for various

reasons. The operation of the protection can cause an islanding condition, also

called a loss-of-mains condition, in which a part of the network, that is, an island fed

by the power station, is isolated from the rest of the network. There is then a risk

of an autoreclosure taking place when the voltages of different parts of the network

do not synchronize, which is a straining incident for the power station. Another risk

is that the generator can lose synchronism during the network fault. A sufficiently

fast trip of the utility circuit breaker of the power station can avoid these risks.
The lower the three-phase symmetrical voltage of the network is, the higher is the

probability that the generator loses the synchronism. The positive-sequence voltage

is also available during asymmetrical faults. It is a more appropriate criterion for

detecting the risk of loss of synchronism than, for example, the lowest phase-to-

phase voltage.
Analyzing the loss of synchronism of a generator is rather complicated and requires

a model of the generator with its prime mover and controllers. The generator can be

able to operate synchronously even if the voltage drops by a few tens of percent for

some hundreds of milliseconds. The setting of PSPTUV is thus determined by the

need to protect the power station from the risks of the islanding conditions since

that requires a higher setting value.
The loss of synchronism of a generator means that the generator is unable to

operate as a generator with the network frequency but enters into an unstable

condition in which it operates by turns as a generator and a motor. Such a condition

stresses the generator thermally and mechanically. This kind of loss of synchronism

should not be mixed with the one between an island and the utility network. In the

islanding situation, the condition of the generator itself is normal but the phase

angle and the frequency of the phase-to-phase voltage can be different from the

corresponding voltage in the rest of the network. The island can have a frequency of

its own relatively fast when fed by a small power station with a low inertia.
PSPTUV complements other loss-of-grid protection principles based on the

ABB RELION REX640, Техническое руководство, Страница: 882 / 1960

Результаты поиска

Содержание RELION REX640

Отзывы: