Basler Electric BE1-87B - Manual (Page 19)

SECTION 2
• APPLICATION
Application
The BE1-87B solid-state, high-speed, high-impedance differential relay is available in single or three-
phase models. The relay was specifically designed to provide high-speed differential protection for high
voltage buses, critical medium, and low voltage buses. Because of its design and sensitivity, the relay can
also be used for shunt reactor protection. While bus schemes require three-phase protection, shunt
reactors may be protected with only one single-phase relay for ground faults. Regardless of the scheme
employed or the equipment protected, the following applications apply to the BE1-87B relay.
Application with Lightning Arresters
The BE1-87B is a high-speed relay designed to operate in a half-cycle or less. As a result, applying the
relay to a bus with lightning arresters must be addressed. The relay pickup current range is adjustable
between 0.25 to 2.5 amperes rms. If lightning arresters will be connected to the bus, use the 2.5 ampere
sensitivity setting so as to prevent the possibility of a differential operation during a normal arrester
operation. If no lightning arresters are used, start with the 0.5 ampere sensitivity setting and adjust as the
application dictates.
CAUTION
If lightning arresters are added to an existing bus, as might be the case when
adding a transformer, be sure to increase the Pickup Current setting of the
BE1-87B to the 2.5 ampere setting.
Application with a Lockout Function
Contacts from the lockout relay (86) should be connected across terminals 5 and 6 (single-phase or
phase A for 3-phase models), 3 and 4 (phase B), and 1 and 2 (phase C) of the BE1-87B relay to short-
circuit the SCRs in the input circuit after a trip output has been initiated. This allows the relay to continue
operation as a conventional overcurrent relay and at the same time protect against exceeding the short-
time rating of the internal SCRs. The relay can be used in any application where the total secondary
current is not more than the current waveform of a fully-offset fault with 215 amperes rms symmetrical
available, provided the lockout relay (86) has an operate time of 1 cycle or less (16 milliseconds).
CAUTION
If the BE1-87B relay control power (power supply voltage) is removed, relay
terminals 5 and 7 (single-phase model) or 5 and 7, 3 and 7, and 1 and 7
(three-phase model) should be shorted by pulling the connection plug. If this is
not done, the BE1-87B relay could be damaged due to continuous fault current
flowing through the relay SCRs.
Current Source for High Impedance Differential Relaying
Predictable current transformer (CT) performance is critical to the effective operation of a high impedance
differential scheme. Where practical, the following current transformer guidelines should be applied when
using the BE1-87B relay.
•
All CTs should be of toroidal design and be fully distributed around the core.
•
All CTs should have the same full ratio value and be connected to the full ratio taps.
•
All CTs should have the same voltage rating, accuracy class, and thermal rating.
•
The CTs should be dedicated to the differential application.
•
When adding to an existing differential scheme, at least one set of CTs in the new breaker should be
ordered with the same ratio and accuracy class as the differential CTs used in the existing scheme.
•
CTs cannot have primary or secondary voltage limiting devices, as the resulting short-circuit could
cause an unwanted operation of the differential.
9282300990 Rev P BE1-87B Application 2-1