Base Quantities For Cvgapc Function; Built-In Overcurrent Protection Steps - ABB Relion 670 Series Technical Reference Manual

Section 9
Multipurpose protection
9.1.2.2
9.1.2.3
272

Base quantities for CVGAPC function

The parameter settings for the base quantities, which represent the base (100%) for
pickup levels of all measuring stages, shall be entered as setting parameters for
every CVGAPC function.
Base current shall be entered as:
1. rated phase current of the protected object in primary amperes, when the
measured Current Quantity is selected from 1 to 9, as shown in table 168.
2. rated phase current of the protected object in primary amperes multiplied by
√3 (1.732 · Iphase), when the measured Current Quantity is selected from 10
to 15, as shown in table 168.
Base voltage shall be entered as:
1. rated phase-to-earth voltage of the protected object in primary kV, when the
measured Voltage Quantity is selected from 1 to 9, as shown in table 169.
2. rated phase-to-phase voltage of the protected object in primary kV, when the
measured Voltage Quantity is selected from 10 to 15, as shown in table 169.

Built-in overcurrent protection steps

Two overcurrent protection steps are available. They are absolutely identical and
therefore only one will be explained here.
Overcurrent step simply compares the magnitude of the measured current quantity
(see table 168) with the set pickup level. Non-directional overcurrent step will
pickup if the magnitude of the measured current quantity is bigger than this set
level. Reset ratio is settable, with default value of 0.96. However depending on
other enabled built-in features this overcurrent pickup might not cause the
overcurrent step start signal. Start signal will only come if all of the enabled built-
in features in the overcurrent step are fulfilled at the same time.
Second harmonic feature
The overcurrent protection step can be restrained by a second harmonic component
in the measured current quantity (see table 168). However it shall be noted that this
feature is not applicable when one of the following measured currents is selected:
• PosSeq (positive sequence current)
• NegSeq (negative sequence current)
• UnbalancePh (unbalance phase current)
• UnbalancePh-Ph (unbalance ph-ph current)
This feature will simple prevent overcurrent step start if the second-to-first
harmonic ratio in the measured current exceeds the set level.
1MRK 505 208-UEN B
Technical reference manual