**Amplifiers/Converters**

# Testing the timing characteristic of the BE1-87T

**Keywords:power
**

/ARTICLES/2002MAY/2002MAY13_POW_DA_AN.PDF |

Published for the Basler Electric Power Systems Group #PC-87T01 7 August 1998
APPLICATION
i
Notes
Testing theTiming Characteristic of the BE1-87T
Scope
The operating and timing characteristics of the
87T relay are displayed in per unit values in the instruc-
tion manual, 9 1713 00 990. This normalizing method
greatly simplifies the presentation of the characteristics,
but tends to be confusing when users need to calculate
actual currents for testing the relay. The following
additional information and examples will clarify the
relationship among the test current, the multiple of tap,
and the multiple of pickup used in the timing character-
istic of Figure 1-3.
Timing Test - Single Input
Principle
This is the simplest and most accurate method to
verify the trip timing of the relay. A test current is
applied between any phase and corresponding com-
mon. The closing time of the trip contact is expected to
be near the values shown in Figure 1-3 which defines
the operating time as a function of multiple of pickup.
This Multitude of Pickup is not be be confused with the
Multiple of Tap. For the single phase test, the operate
and restraint currents are equal : the test current as a
multiple of tap is It=k.Tap, where k is the multiple of
tap. Also : Iop = k.Tap since the operate and restraint
currents are equal in this case. The Minimum Pickup
(MPU) defining the boundary between the operate and
restrain region in Figure 1-2, for test currents greater
than the intersection of the slope line with the Iop=.35
line, is : MPU=(slope)x(multiple of tap) xTap. The
multiple of pickup (m) is therefore: m=Iop/
MPU=k.Tap/s.k.Tap=1/s. In other words, the multiple
of pickup of the test current for single phase testing is
always 1/s, regardless of its multiple of tap value.
Test current selection
Let's say that it is desired to measure the response
time at 2X Multiple of Tap for a slope setting of s=0.3
(30%). The MPU is (s)x(multiple of tap)xTap for
(multiple of tap)>0.35/(slope). The multiple of pickup is
1/.3=3.3.
For a tap of 2A, It=2x2=4A;
MPU=0.3x2x2=1.2A; m=4/1.2=3.3.
Expected time
The timing characteristic shown in Instruction
Manual Figure 1-3 represents the total response time as
a function of multiple of pickup for a typical relay. For
the given example, the expected trip time, correspond-
ing to m=3.3, is about 32ms.
Timing Test - Two Inputs
Principle
A restraint current is applied between the same
phase and its corresponding common on two input
circuits. The currents are adjusted for a given multiple
of tap on each circuit, at the proper phase to yield a
balanced condition, i.e. the operate current is zero. One
of the currents is then reduced to a value that yields an
operate current equal to the desired multiple of pickup
for which the response time is desired.
Test current selection
Let's say that the following taps have been set:
Circuit 1: Tap=2A Circuit 2: Tap=11.7A
Slope=30%
Assume that the test is to be performed at a
restraint value of 2xTap.
The initial (balanced) current is thus 4A and 23.4A
for each circuit. Note that the current in one circuit
exceeds the continuous rating of 20A; the maximum
ON time must take this fact into account.
For best results, the operate current is obtained by
lowering the current in one circuit. This assures the
maximum restraint current remains equal to the desired
multiple.
The Minimum Pickup (MPU) is derived from the
percent restraint characteristic (Figure 1-2). At 2xTap
and a slope of 30%, the MPU is equal to the (maximum
restraint) x(slope), in multiples of tap. To obtain an
operate current of a multiple of pickup (m) at the
restraint current of k.Tap, the test current in one of the
circuits must be reduced to It=k.Tap.(1-m.s). See
Table1.
When the current in circuit 2 is reduced from the
balance value of 23.4A, pickup occurs below 23.4-
(23.4x.3)=16.36A. To obtain an operate current of
2xMPU for the timing test, the test current must be
PC-87T01 (8/98)
Definitions k=multiple of tap restraint (Fig.1-2) =Irest(max)/tap
m=multiple of pickup (Fig.1-3) =Iop/MPU
s=slope (p.u.)
Tap: relay setting
SINGLE SOURCE TWO SOURCES
Test current:
increase (step) for k>0.35/s : It=k.Tap
from 0 to It m=1/s
Test current:
Reduce (step) It = k.Tap (1-m.s)
from balance
(k.Tap) to It
Table 1
Note: For two source testing using the current reduction method, the maximum multiple of
pickup is reached when It=0. In this case m=1/s, as in the single input test.
Figure 1-2, simplified. Figure 1-3, simplified.
reduced from 23.4 to 23.4-2x(23.4x.3)=23.4x(1-
2x.3)=9.36A.
Expected time
The operate time corresponding to this multiple
of pickup of 2 is found in Figure 1-3 : 52ms. Variations
of about 25% are to be expected, due to component
tolerances, but particularly due to the slope of the
characteristic at multiples of pickup below 3.
Conclusion
Figures 1-2 and 1-3 have been simplified (below)
to clarify the testing concepts.
The test currents can be calculated for other tap
and slope combinations from the following summary,
Table 1.
ROUTE 143, BOX 269, HIGHLAND, ILLINOIS U.S.A. 62249
PHONE 618-654-2341 FAX 618-654-2351
P.A.E. Les Pins, 67319 Wasselonne Cedex FRANCE
PHONE (33-3-88) 87-1010 FAX (33-3-88) 87-0808
http://www.basler.com, [email protected]

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