Ampcontrol Pty Ltd
– ABN 28 000 915 542
IPD USER MANUAL
IPDB014 Version 14
– SEP/2020
Uncontrolled Copy - Refer to Ampcontrol Website for Latest Version
Page 50 of 96
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10.4 Phase Current Balance
Phase current balance protection is selected via the “Cur Bal Trp” selection (See Section 13, User
Adjustable Settings). The current balance measurement is displayed on the Remote Display Module and
is calculated as:
𝐼
𝑏𝑎𝑙
=
𝑀𝐴𝑋 ∆ 𝐼 × 100%
𝐼
𝑎𝑣𝑒
Where:
I
ave
= Average of the 3 phase currents
MAX
∆I = The maximum deviation of a phase current from the average
The trip level is selectable at 5%, 10%, 20%, 50% and off.
The phase current balance protection is inhibited until the average current exceeds both 20% of the
selected full load current and the selected balance trip level.
If the trip level is exceeded, a timer is triggered. If the imbalance remains above the set level for more
than two seconds the relay trips. The event log records “Ibal” to differentiate it from a true over-current
trip.
The status of the timer is displayed adjacent to the “Ibal” value (Level 5, Position 2). A trip condition
occurs when the timer reaches 100%.
10.5 Transient Overreach Compensation
Transient overreach is a phenomenon experienced by overcurrent relays where a measured AC signal is
offset by a decaying DC component (see figure below, taken from IEC 60255-151). The effect is typically
caused by a step change in the measured signal, such as at contact closure for a direct-online motor.
Figure 10.2: Transient Overreach During Contactor Closure (Source: IEC 60255-151)
