Basler BE1-60 Voltage Balance Relay Setting Test

Engineering application of Basler BE1-60 voltage balance relay in generator PT disconnection protection and overcurrent lockout

In power plants and substations, the disconnection or failure of the secondary circuit of voltage transformers (PT) is one of the common hidden dangers that can cause protective devices to malfunction. Once the PT fuse is blown or the circuit contact is poor, equipment such as voltage control/voltage limiting overcurrent relays, impedance relays, synchronous relays, excitation regulators, etc. may mistakenly send trip signals due to sensing incorrect voltage, causing unplanned shutdown of the unit or even equipment damage. The BE1-60 voltage balancing relay from Basler Electric is a fast response component specifically designed to solve such problems. Starting from engineering practice, this article systematically sorts out the functional principles, selection points, on-site wiring, setting strategies, and testing verification methods of the relay, providing an operable reference document for electrical maintenance and relay protection personnel.

Product positioning and typical protection scenarios

BE1-60 belongs to the voltage balance relay, and its core task is to continuously compare the difference between two three-phase voltages (usually the power PT secondary voltage and the measured PT secondary voltage). When the voltage difference of any phase exceeds the preset threshold, it quickly sends an alarm or lockout signal to prevent the downstream protection device from malfunctioning due to PT disconnection. This relay is particularly suitable for the following scenarios:

When a generator equipped with a static excitation system experiences a power PT or measurement PT disconnection, the excitation system may output over excitation or under excitation due to abnormal voltage feedback. BE1-60 can distinguish the fault location and initiate the corresponding shutdown or alarm process.

Locking of voltage controlled or voltage limited overcurrent relay: When the sensitivity of the overcurrent relay is abnormally increased due to PT disconnection during measurement, BE1-60 disconnects the tripping circuit of the overcurrent relay through its normally closed contact to avoid false tripping.

Impedance protection, synchronization devices, voltage regulators, and other equipment that require high voltage integrity can all achieve reliable PT disconnection locking through the auxiliary output contacts of BE1-60.

Working principle and signal flow

BE1-60 receives two three-phase voltages (referred to as circuit 1 and circuit 2 respectively) through a step-down transformer internally. After full wave rectification and integration of each phase voltage, a DC level representing the amplitude of that phase voltage is obtained. Next, a dedicated differential amplifier compares the same phase of the two signals and calculates the voltage difference. The difference is compared with the threshold set on the panel (5%~50% rated value, step size 5%). If it exceeds the limit, the corresponding output relay will be triggered.

The noteworthy details are:

The two circuits are independently monitored, and the action direction of the output relay points to the side with lower voltage. For example, if the voltage of one phase of circuit 1 is lower than the corresponding phase of circuit 2, the output relay of circuit 1 will be excited (indicating that there is an undervoltage fault in circuit 1).

When the voltage difference returns below the threshold, the relay will not immediately reset, but will have a fixed delay of about 0.75 seconds to prevent frequent actions caused by transient fluctuations.

For input types (E-type and F-type) that use Scott transformers (T-connection), the three-phase voltage is internally synthesized into a single-phase quantity proportional to the average value. At this time, the sensitivity of the relay will be reduced, and a lower setting gear needs to be selected.

Interpretation of Model Code and Key Points for Selection

The model code of BE1-60 consists of multiple fields, and a correct understanding is beneficial for precise selection. Taking the example model D1H-A1R-C0C2F as an example, the meanings of each field are as follows:

D: Inductive input type, three-phase star (Wye) input converted to three-phase delta internal connection, suitable for 208V line voltage system; There are also options such as A (single-phase), B (three-phase star), C (three-phase delta), E (single-phase to three-phase star), F (single-phase to three-phase delta), etc.

1: The induction range, which is 60% to 125% of the rated voltage, is usually matched with the secondary voltage of the system PT.

H: Output relay configuration, in this example, there are two normally closed (NC) outputs, one for each circuit; Other options include normally open or mixed.

A1: Timing characteristic, here it is instantaneous action (<150ms).

R: Control power type, 24 Vdc (low range), also available O（48/125Vdc）、P（125Vdc/120Vac）、S（48/125Vdc）、T（250Vdc/240Vac） Wait.

C: Target indicator type, internal excitation type (can light up without external current), optional current type or none.