Introduction
This manual
The technical manual contains application and functionality descriptions and lists function blocks, logic diagrams, input and output signals, setting parameters andtechnical data sorted per function. The manual can be used as a technical reference during the engineering phase, installation and commissioning phase, and during normal service.
500CIM06 1MRB150077R0111
500CIM06 1MRB150077R0112
500CPU05 1MRB150081R0001
500BIO01 1MRB150005R0001
500PSM03 1MRB150038R0001
500SCM01 1MRB150004R0001
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Intended audience
This manual addresses system engineers and installation and commissioning personnel, who use technical data during engineering, installation and commissioning, and in normal service.
The system engineer must have a thorough knowledge of protection systems, protection equipment, protection functions and the configured functional logic inthe IEDs. The installation and commissioning personnel must have a basic knowledge of handling electronic equipment.
Mode of operation
The circuit-breaker is the last and most important link in the protection chain. The purpose of BFP is to take the right action should the circuit-breaker fail to execute a trip command. This involves tripping the circuit-breakers surrounding the fault, which are mainly in the same station, but may also include circuit-breakers at the remote ends of lines (intertripping).
The principle of BFP is based on monitoring the time the fault persists after a trip command has been issued to the circuit breaker (the start of BFP has been enabled by the main protection, e.g. feeder protection).
A complete block diagram of BFP, including additional functions such as initiation logics and I0-measurement, can be seen in Figure 8.
The following internal REB500 functions can start the breaker failure function in all three phases:
• REB500 intertripping system (BBP, BFP, etc.)
• An external trip command
• Time-overcurrent if logic 3 is configured
• Breaker pole discrepancy protection if logic 3 is configured
BFP can be started phase-selectively via two separate inputs. All three phases can be started via up to 6 different inputs, and the currents of all three phases are monitored.
This setting applies to phase faults und ground faults as well under the condition that reflects the minimal short circuit current out of these fault types. In certain cases, the ground fault current may be much lower than the phase fault value (e.g. low resistive grounded networks). Under such exceptional cases, the BFP Io (adjusted with a lower pickup value) can be used in addition to the breaker failure phase system (see Section 5.2)
Operation of BFP can also be started by the internal signals. These internal signals are shown with the following symbol in the block diagram of BFP. The inputs are on the left and the outputs on the right.
Configuration
BFP has two adjustable timers. At the end of time t1, a second attempt is made to trip the breaker that has failed to trip; at the end of time t2, the surrounding breakers are tripped. A transfer-tripping signal to the remote station generated either at the end of time t1 or t2 can also be enabled using HMI500.
The currents of the three phases are measured individually and compared with the pick-up setting, which is identical for the three phases.
Since there are three separate t1 timers for the individual phases, the REB500 BFP responds correctly to an evolving fault.
Logic 4 can be used in stations with 2 redundant REB500 units, one for busbar and the other for breaker failure protection. In this case, the special inputs “13760_Start BFP L1L2L3_5” and “13765_Start BFP L1L2L3_6” on the REB500 for BFP are used to instantly initiate intertripping after t1 independently of the time setting of t2.
Mode of operation
Certain network configurations (e.g., impedance-grounded networks) might cause fault currents that are below the normal load current. While protection devices such as sensitive earth fault protections or similar are still starting and tripping the breaker, the conventional BFP is usually set at levels above normal load currents for the phase systems. In such situations, a separate setting for the neutral current I0 might be helpful.
Detailed knowledge of the network, the protection systems and possible fault scenarios is necessary to configure this function correctly. Misconfiguration might lead to unselective tripping and loss of supply.
The BFP L0 system is an integrated part in the conventional BFP function that can be activated and configured separately.
The neutral measuring system of BFP for I0 covers the ground potential as a fourth phase and evaluates breaker failure conditions accordingly. To allow for individual fault handling, separate configuration for the I0 threshold and timer stage t1 is possible.
When activated, the function is completely integrated into the existing BFP function. With the exceptions mentioned above, both timer t2 and the intertripping system are used by the BFP phase and L0 system.
The following diagram shows a simplified representation of the extension of the conventional BFP system with the L0 system.
