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.

0: No power status output, optional 1 is with power status output.

C: Output test button with push to test button.

2: Auxiliary output type, normally closed (NC) auxiliary contact, one for each circuit.

F: Shell form, semi embedded installation.

When selecting, it is important to pay attention to whether the input voltage level and wiring method (star or delta) are consistent with the on-site PT; The output contact form (normally open/normally closed) needs to meet the requirements of the interlocking circuit (usually requiring normally closed series connection to the trip circuit); The control power supply voltage needs to match the on-site DC or AC power supply.

Key points for installation wiring and grounding

BE1-60 adopts S1 chassis and supports semi embedded or protruding installation. The installation dimensions and panel opening diagram are detailed in the manual (in inches and millimeters). Due to the solid-state design of the relay, there are no special restrictions on the installation angle.

Key Wiring Guide:

Voltage input terminal: According to the induction input type (A~F), connect the two three-phase voltages to the corresponding terminal blocks according to Figure 4-8 in the manual. For example, a three-phase star input needs to be connected to the A, B, C phases and neutral point (if any), while a delta input needs to be connected to the line voltage.

Output contact: The main output (loop 1 and loop 2) is usually used for trip locking or alarm. If used for blocking overcurrent relays, the normally closed contacts should be connected in series in the overcurrent relay trip outlet circuit.

Auxiliary power supply: The power terminals have no polarity, but it is necessary to ensure that the voltage is within the allowable range. When the power supply is normal, the green LED on the panel lights up.

Grounding: A copper wire of not less than 12 AWG must be used to reliably connect the grounding terminal of the enclosure to the ground grid, and it is recommended that each device be independently led to avoid common ground interference.

Important precautions:

If the output contact drives the external relay coil, it is recommended to parallel reverse diodes at both ends of the coil to suppress EMI interference.

If insulation withstand voltage testing is required, the connecting plug must be unplugged and the relay must be removed from the chassis first, otherwise it may damage the internal electronic components.

Setting strategy and typical settings

The only user setting component for BE1-60 is the ten level differential setting switch on the panel, corresponding to 5% to 50% rated voltage, with a step size of 5%. Reasonable tuning should take into account the following factors:

The inherent deviation of the two PTs during normal operation: Due to the fact that the power PT and measurement PT may be taken from different positions, there may be a 2% to 5% difference in their secondary voltage during load changes. For example, when the generator is fully loaded, the power PT voltage may be 5% lower than when it is unloaded, so the set value should be greater than the maximum normal deviation, usually taking 10% to 15% as the starting point.

For E/F type input (single-phase synthesis): Due to internal averaging processing, the actual sensitivity is reduced. It is recommended to use a lower gear (such as B=10% or C=15%), otherwise single-phase disconnection may not be detected.

Coordination with other protections in the system: If used to block voltage controlled overcurrent relays, it is necessary to ensure that BE1-60 can send a blocking signal before the overcurrent relay acts when the voltage drop caused by PT disconnection reaches the set value. Due to the BE1-60 action time being less than 150ms, which is much faster than the timing or inverse time limit of the overcurrent relay, it usually meets the coordination requirements.

Example calculation: Assuming the rated voltage of the system is 120Vac and the normal voltage difference between the power PT and the measured PT does not exceed 8%, the setting switch can be set to C (15%) or D (20%), leaving sufficient margin. If using E/F type input, it is recommended to place it at B (10%), because the equivalent difference synthesized internally during single-phase disconnection is only one-third of the actual phase voltage difference (such as the 40V synthesized difference mentioned above). If placed at G (42V), it may not function.

On site testing and functional verification

After new installation or maintenance, it is recommended to perform functional testing according to the following steps to verify that the relay wiring is correct and the setting is reasonable.

Required instruments: Adjustable three-phase or single-phase AC voltage source (accuracy ± 1%), multimeter, timer.

6.1 Basic Actions and Reset Test (Taking Three Phase Star Input as an Example)

Set the difference setting switch to the lowest gear A (5%).

Apply rated voltage (such as 120Vac line voltage) to both inputs, wait for the state to stabilize, confirm that both output relays are in normal state (normally closed type is closed, normally open type is open), and reset the target indicator (if any).

Slowly increase the A-phase voltage of circuit 1 (while keeping the other phases rated), and observe when the output relay of circuit 2 shifts (indicating that the voltage of the phase where circuit 2 is located is relatively low). According to the manual, the change point should be between 125~127Vac (i.e. 104~106% of the rated voltage) - because at this point, the difference reaches more than 5%. Record the value and compare it with the theoretical value.

Reduce the phase voltage of circuit 1A back to 120Vac, and the relay should automatically reset (output returns to normal state) after about 0.75 seconds. Reset the target indicator.

6.2 High setting value test (verify setting range)

Set the setting switch to the highest position K (50%).

Slowly reduce the A-phase voltage of circuit 1 (while keeping the other phases rated) until the output relay of circuit 1 shifts (indicating that the voltage of circuit 1 is too low). In theory, the change point should be between 57~63Vac (i.e. 47%~53% of the rated voltage), as the difference reaches about 50% at this time.

Record the change point and calculate whether the error is within the allowable range (± 1V or ± 5% of the set value, whichever is greater).

6.3 Multiphase testing (applicable to three-phase input types B/C/D)

Repeat the above steps and perform single-phase voltage rise and fall tests on phases B and C respectively to ensure that the differential circuit of each phase is working properly.

6.4 Verification of output contacts and target indicators

If equipped with a "push test" button, use a non-conductive rod to press the corresponding test button for circuit 1 or circuit 2, observe whether the corresponding output relay is excited (target on, contact status changes), and verify the integrity of the external wiring circuit.

For current type targets, it is necessary to ensure that the tripping circuit current is not less than 200mA, otherwise the target will not light up.

6.5 System cascading adjustment (actual locking effect)

Under simulated PT disconnection conditions (such as manually disconnecting one phase voltage), observe whether BE1-60 can issue a lockout signal before the overcurrent relay acts. An oscilloscope or event recorder can be used to capture the timing of actions, ensuring that the locking contact opens before the tripping contact.

Maintenance and Storage Suggestions

BE1-60 is a solid-state relay with extremely low daily maintenance requirements. It is recommended to conduct a complete functional test once a year to confirm that the setting values and action times are still within the specifications. If the relay is kept in stock for a long time, it should be powered on for 30 minutes every year to maintain the performance of the internal electrolytic capacitor and extend its service life. In case of malfunction, on-site dismantling and repair should not be carried out, and Basler Electric technical support should be contacted in a timely manner.