Schweitzer Engineering SEL-387-0, Инструкция по эксплуатации

Страница: 178 / 556

5.4
SEL-387-0, -5, -6 Relay Instruction Manual Date Code 20170601
Metering and Monitoring
Metering Functions
The report for MET P contains the last reset times for the peak demand
registers for each winding.
Differential Metering
Function (METER DIF
Command)
This metering function is performed on an element basis, not on a winding
basis, because of the nature of the function. The relay has three differential
elements, one per phase, denoted 87 1, 87 2, and 87 3. The “A-phase” currents
for each winding are compensated for CT and transformer winding
connections, then divided by the tap value for each winding, and entered into
the calculations as dimensionless “multiples of tap.” These values are then
summed in 87 1 on a phasor basis for determining operating current (IOP
k )
and on a scalar magnitude basis for the restraint current (IRT k ) calculation
( k = 1, 2, 3). The B-phase and C-phase values find their way to 87 2 and 87 3,
respectively.
In response to the MET DIF command, the fundamental frequency Operate
and Restraint currents for each differential element are displayed in multiples
of tap. The second- and fifth-harmonic currents in each element are also
shown in multiples of tap. These are calculated in the same way as the operate
currents, using the harmonic current from each winding in a phasor addition.
If the command is typed as
MET DIF m , where m is any number from 1 to
32767, the report will be repeated m times in succession. In this mode,
subsequent reports are not generated until the previous report has been
completely sent. The format for the
MET DIF report is as follows:
=> METER DIF <Enter>
XFMR 1 Date: MM/DD/YY Time: HH:MM:SS.SSS
STATION A
Operate Currents Restraint Currents
IOP1 IOP2 IOP3 IRT1 IRT2 IRT3
I (Mult. of Tap) 123.12 123.12 123.12 123.12 123.12 123.12
Second Harmonic Currents Fifth Harmonic Currents
I1F2 I2F2 I3F2 I1F5 I2F5 I3F5
I (Mult. of Tap) 123.12 123.12 123.12 123.12 123.12 123.12
The quantities I1F2/IOP1, I2F2/IOP2, I3F2/IOP3, and I1F5/IOP1, etc., form
the basis for the harmonic blocking feature. To determine if blocking should
take place, these ratios of harmonic to fundamental operating current (times
100 percent) are compared to the user-selected blocking threshold settings
PCT2 and PCT5.
Phasor Current
Metering Function
(METER SEC
Command)
The phasor current metering function is a useful tool for verifying proper
phase rotation of input currents, for checking CT connections and polarities,
and for checking that “in” currents are about 180° out-of-phase with “out”
currents. With normal load currents on the transformer, the correctness (or
lack thereof) of all the input connections becomes apparent.
In response to the MET SEC command, the separate phase currents, as well
as the positive-sequence, negative-sequence, and residual currents for each
winding, are shown in secondary amperes and at a calculated phase angle. The
relay uses the sample data to calculate the rms phasor magnitudes and
instantaneous phase angles as a kind of “snapshot” of all the phasor currents at
an instant in time. If the command is typed as
MET SEC m , where m is any
number from 1 to 32767, the report will be repeated m times in succession. In
this mode, subsequent reports are not generated until the previous report has
been completely sent. The format for the
MET SEC report is as follows: