9.14.2 Application
A breakdown of the insulation between phase conductors or a phase conductor and
earth results in a short-circuit or an earth fault. Such faults can result in large fault
currents and may cause severe damage to the power system primary equipment.
A typical application of the voltage-restrained time overcurrent protection is in the
generator protection system, where it is used as backup protection. If a phase-to-phase
fault affects a generator, the fault current amplitude is a function of time, and it
depends on generator characteristic (reactances and time constants), its load
conditions (immediately before the fault) and excitation system performance and
characteristic. So the fault current amplitude may decay with time. A voltage-
restrained overcurrent relay can be set in order to remain in the picked-up state in spite
of the current decay, and perform a backup trip in case of failure of the main
protection.
The IED can be provided with a voltage-restrained time overcurrent protection
(VRPVOC). The VRPVOC function is always connected to three-phase current and
three-phase voltage input in the configuration tool, but it will always measure the
maximum phase current and the minimum phase-to-phase voltage.
VRPVOC function module has two independent protection each consisting of:
• One overcurrent step with the following built-in features:
• Selectable definite time delay or Inverse Time IDMT characteristic
• Voltage restrained/controlled feature is available in order to modify the
start level of the overcurrent stage in proportion to the magnitude of the
measured voltage
• One undervoltage step with the following built-in feature:
• Definite time delay
The undervoltage function can be enabled or disabled. Sometimes in order to obtain
the desired application functionality it is necessary to provide interaction between the
two protection elements within the VRPVOC function by appropriate IED
configuration (for example, overcurrent protection with under-voltage seal-in).
Sometimes in order to obtain the desired application functionality it is necessary to
provide interaction between the two protection elements within the D2PTOC function
by appropriate IED configuration (for example, overcurrent protection with under-
voltage seal-in).
9.14.2.1 Base quantities
GlobalBaseSel defines the particular Global Base Values Group where the base
quantities of the function are set. In that Global Base Values Group:
IBase shall be entered as rated phase current of the protected object in primary
amperes.
1MRK 502 071-UEN - Section 9
Current protection
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062 395
Application manual
To Next Page
Loading...
Need help?
General
