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1. The IED_H send a signal to the IED_G at sampling time of IED_H.
2. The IED_G receives this signal.
3. The IED_G replies to the IED_H at sampling time of IED_G.
4. This signal reverts to the IED_H.
As seen from Figure 2.36-4(2), the IED_G can determine the time T
M
with the clock in
the IED_G and the arrival time of this signal. On the other hand, in Figure 2.36-4(4), the
IED_H can determine the time T
F
with the clock in the IED_H. The IED_H also can determine
the arrival time of that signal.
Figure 2.36-5 shows a communication for the protection; the channel is provided at both
the master IED_G and the slave IED_H.
Figure 2.36-5 Communication channel between IEDs
When provided delay time of channel #1 provided by the telecommunication carrier, the
∆T can be obtained from the following equations:
where,
T
M
: Sampling displacement between IEDs on the master IED (T
M
= T
d1
−∆T)
T
F
: Sampling displacement between IEDs on the slave IED (T
F
= T
d2
+∆T)
T
d1
: Propagation time of the downstream line
T
d2
: Propagation time of the upstream line
Sampling pulses are generated by the clock in the slave IED_H; hence, the slave IED_H
can carry out its sampling in advance on its discretion because the slave IED_H can vary its
sampling interval with its own clock. As a result, the slave IED_H move its sampling time in
advance based on the ∆T calculated with equation (2.36-1); and the ∆T of the master IED_G
can be close to zero. The slave IED_H can of course reduce its sampling time with equation
Downstream line with propagation delay
Upstream line with propagation delay
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