With our example con guration the calculation would be:
Now this value presents the transformer properties maximum caused differential current to nominal.
Other uncertainties known now may be added to this got value and after this operation can be said
that:
This means that in worst case this differential current will flow while the operation is still normal in the
transformer. Therefore normally this got combined result is increased with safety marginal to ensure
stabile operation of the differential protection and to negate possible calculation errors.
With these values following base sensitivity (e.g. the minimum setting for the differential current
required to operate the relay), is given for the differential protection characteristics:
Now this basic sensitivity is taking account the starting situation with no load to Turnpoint 1 in the
characteristics. Next thing is to decide where to set the Turnpoint 1. In most of differential relays this
point is either xed or automatically de ned based on base sensitivity and slope 1. In this IED type
differential relay it is settable. For high sensitivity it may be set to 1 xIn since the calculated base
sensitivity takes into account already the tap changer effect and all of the other normal operating
caused differential current sources.
For coarse settings this Turnpoint 1 can be set to for example 0.5xIn or even 0.01xIn. How to
determine this limit is the sum of the protection principle wanted. Smaller value leads to conservative
and stabile operation, while bigger means highly sensitive and possibly unstable protection.
Also there if Turnpoint 1 is set to 0.01xIn, the Slope 1 will start directly from the setting. In such case
there is no unbiased sensitive section available. This could be used in case when the tap changer
effect is not wanted to be taken into account for basic sensitivity and the effect is wanted to be taken
into account in the rst slope directly. This can lead to optimal sensitivity and stabile settings for
differential relay even there is no non biased sensitive section in the characteristics.
In this case the base sensitivity setting should be set as follows:
Now the Slope 1 settings, this part presents the relay restraint characteristics over the load current
range of the transformer. This slope should be effective up to the maximum possible loading of the
transformer. Normally for power transformer this value should be about 1.0 – 2.0xIn (for large power
transformers) when typical value would be 1.5xIn. The functionality purpose is to compensate
measurement errors caused by relative high current with the tap changer effect included. Slope 1 is
calculated by using the transformer and CT nominal values in the maximum full load (Turnpoint 2) of
the transformer with highest possible differential current causing tap position. Generally Slope 1 setting
is calculated as below:
AQ-T216
Instruction manual
Version: 2.00
© Arcteq Relays Ltd
134
Содержание AQ 200 Series
Страница 1: ...AQ T216 Transformer protection IED Instruction manual ...
Страница 243: ...Figure 7 1 162 AQ T216 variant with binary input modules AQ T216 Instruction manual Version 2 00 Arcteq Relays Ltd 242 ...
Страница 264: ...Figure 8 11 184 Panel cut out and spacing of the IED AQ T216 Instruction manual Version 2 00 263 Arcteq Relays Ltd ...
Страница 284: ...10 Ordering information AQ T216 Instruction manual Version 2 00 283 Arcteq Relays Ltd ...
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