Technical Guide
Testing self-powered relays with SVERKER 900
Page 8(33)
Figure 4. The 6 standardized IEC curves in IEC 60255-151:2009. From IEC 60255-151:2009 ed.1.0 -
“Copyright
© 201x IEC Geneva, Switzerland.
4.1.2.
The “Time Multiplier”, TMS.
Many names have always been given to the so-called
time multiplier, known as “k factor”, “alpha factor”, “a
factor” etc.
The standardized name according to IEC 60255-151 is TMS: Time Multiplier Setting, or simply Time Multiplier.
4.1.3. Testing the start value and the operate time.
In the IEC 60255-1xx series of standards for protection functions there is always the difference between two
basic test methods:
1)
Test of the “border” of the characteristics
2) Test of the operate time of the characteristic
For the test of the border, it is intended to verify the accuracy of the border of the relay characteristic. For
overcurrent relays the characteristic is defined by the
“start value” (“pick-up” value
5
): the current threshold above
which the protection relay starts the timer for the trip command, according to a defined formula where the
operate time is function of the current level. Below this start
value (often denoted as “I>” or “I>>”), the protection
relay does not react. In IEC 60255-
151 this “start value” is called Gs.
5
Note that in IEC world it is usually used the name “start” (start time, start contact etc.), while in the ANSI/IEEE world it is
often used the name “pick-up” (pick-up time, pick-up contact etc). At the same time, for tripping, the IEC world should use
the name “operate” (operate time, operate contact) while the ANSI/IEEE world uses the name “trip” (trip time, trip contact).
In this document
we will use indifferently the terms “start” and “pick-up” and/or “operate” and “trip”.
