ABB RELION 670 SERIES REG670 - Overexcitation Protection OEXPVPH (24); Identification; Application

10.4 Overexcitation protection OEXPVPH (24)
IP14547-1 v3
10.4.1 Identification
M14867-1 v3
Function description IEC 61850
identification
IEC 60617
identification
ANSI/IEEE C37.2
device number
Overexcitation protection OEXPVPH
U/f >
SYMBOL-Q V1 EN-US
24
10.4.2 Application
M13785-3 v6
When the laminated core of a power transformer is subjected to a magnetic flux density
beyond its design limits, stray flux will flow into non-laminated components not
designed to carry flux and cause eddy currents to flow. The eddy currents can cause
excessive heating and severe damage to insulation and adjacent parts in a relatively
short time.
Overvoltage, or underfrequency
, or a combination of both, will result in an excessive
flux density level, which is denominated overfluxing or over-excitation.
The greatest risk for overexcitation exists in a thermal power station when the
generator-transformer block is disconnected from the rest of the network, or in network
“islands” occuring at disturbance where high voltages and/or low frequencies can
occur. Overexcitation can occur during start-up and shut-down of the generator if the
field current is not properly adjusted. Loss-of load or load-shedding can also result in
overexcitation if the voltage control and frequency governor is not functioning
properly. Loss of load or load-shedding at a transformer substation can result in
overexcitation if the voltage control function is insufficient or out of order. Low
frequency in a system isolated from the main network can result in overexcitation if the
voltage regulating system maintains normal voltage.
According to the IEC standards, the power transformers shall be capable of delivering
rated load current continuously at an applied voltage of 105% of rated value (at rated
frequency). For special cases, the purchaser may specify that the transformer shall be
capable of operating continuously at an applied voltage 110% of rated value at no load,
reduced to 105% at rated secondary load current.
According to ANSI/IEEE standards, the transformers shall be capable of delivering
rated load current continuously at an output voltage of 105% of rated value (at rated
frequency) and operate continuously with output voltage equal to 110% of rated value
at no load.
Section 10 1MRK 502 071-UUS A
Voltage protection
454 Generator protection REG670 2.2 ANSI and Injection equipment REX060, REX061, REX062
Application manual