Areva MiCOM P441, Technical Manual

Page: 264 / 636

P44x/EN AP/E33 Application Notes
Page 90/220 MiCOM P441/P442 & P444
2.19 Undervoltage protection
Undervoltage conditions may occur on a power system for a variety of reasons, some of
which are outlined below:-
•
Increased system loading. Generally, some corrective action would be taken by
voltage regulating equipment such as AVR’s or On Load Tap Changers, in order to
bring the system voltage back to it’s nominal value. If the regulating equipment is
unsuccessful in restoring healthy system voltage, then tripping by means of an
undervoltage relay will be required following a suitable time delay.
•
Faults occurring on the power system result in a reduction in voltage of the phases
involved in the fault. The proportion by which the voltage decreases is directly
dependent upon the type of fault, method of system earthing and its location with
respect to the relaying point. Consequently, co-ordination with other voltage and
current-based protection devices is essential in order to achieve correct discrimination.
This function will be blocked with VTS logic or could be disabled if CB open.
Both the under and overvoltage protection functions can be found in the relay menu “Volt
Protection”. The following table shows the undervoltage section of this menu along with the
available setting ranges and factory defaults.
Menu text Default setting Setting range Step size
Min Max
GROUP 1
VOLT Protection
V< & V> MODE 0 V<1 Trip, V<2 Trip, V>1 Trip, V>2 Trip
UNDER VOLTAGE
V< Measur't Mode Phase-Neutral Phase-phase or Phase-neutral
V<1 Function DT Disabled, DT pr IDMT
V<1 Voltage Set 50V 10V 120V 1V
V<1 Time Delay 10s 0s 100s 0.01s
V<1 TMS 1 0.5 100 0.5
V<2 Status Disabled Disabled or Enabled
V<2 Voltage Set 38V 10V 120V 1V
V<2 Time Delay 5s 0s 100s 0.01s
As can be seen from the menu, the undervoltage protection included within the P441, P442
and P444 relays consists of two independent stages. These are configurable as either
phase to phase or phase to neutral measuring within the V< Measur’t Mode cell.
Stage 1 may be selected as either IDMT, DT or disabled, within the V<1 Function cell.
Stage 2 is DT only and is enabled/disabled in the V<2 Status cell.
Two stages are included to provide both alarm and trip stages, where required.
Alternatively, different time settings may be required depending upon the severity of the
voltage dip.
The IDMT characteristic available on the first stage is defined by the following formula:
t =
K
1 – M
Where:
K = Time Multiplier Setting (TMS)
T = Operating Time in Seconds
M = Measured Voltage / relay Setting Voltage (V<)