ABB Relion 670 series, Technical Reference Manual, Page: 367 / 1232

to each other can be separated with the line/s closest to the centre of the power swing
allowing the two systems to be stable as separated islands.
6.13.2 Principle of operation
If the generator is faster than the power system, the rotor movement in the impedance
and voltage diagram is from right to left and generating is signalled. If the generator is
slower than the power system, the rotor movement is from left to right and motoring is
signalled (the power system drives the generator as if it were a motor).
The movements in the impedance plain can be seen in figure 192 . The transient
behaviour is described by the transient EMF's E
A
and E
B
, and by X'
d
, X
T
and the
transient system impedance Z
S
.
1MRK505222-UUS C
Section 6
Impedance protection
361
Technical reference manual