Basler BE1-40Q demagnetization relay setting test

Analysis of the entire process of setting calculation and on-site testing for Basler BE1-40Q demagnetization relay

The demagnetization protection of synchronous generators is a crucial part of the generator protection system. When the excitation system fails or operates under excitation, the generator may absorb a large amount of reactive power, resulting in rotor overheating, stator end heating, and even step loss, seriously threatening the safety of the unit. The BE1-40Q demagnetization relay of Basler Electric monitors the flow and amplitude of reactive power (var) at the generator end, and quickly acts in the early stage of demagnetization to avoid equipment damage. This article combines the technical manual of the relay to systematically analyze its principles, selection, installation and wiring, setting calculation, and on-site testing methods from an engineering application perspective, providing a practical operation guide for relay protection engineers.

1. Principle of demagnetization protection and action characteristics of BE1-40Q

When a synchronous generator operates normally, it is usually in an overexcitation state and emits reactive power (lagging power factor) to the system. When the excitation current decreases or disappears, the generator begins to absorb reactive power from the system (leading operation), and the rotor magnetic field weakens, increasing the risk of breaking the static stability limit sharply. If the reactive power reserve of the system is sufficient, the generator may enter asynchronous operation, and slip frequency current may be induced in the rotor damping winding, which can cause severe heating in a short period of time.

BE1-40Q adopts the measurement principle based on the voltage current phasor relationship, calculates the reactive power by multiplying the single-phase voltage (V_AB) and single-phase current (I2) and their phase angles, and sends out a trip signal when the reactive power exceeds the set value. The operating characteristics of this relay are manifested on the complex power plane as a straight line at an angle of 8 ° to the horizontal axis, which is placed outside the allowable operating zone of the generator (usually below the static stability limit curve or below the stator end heating limit curve). The set value is the intersection point between the line and the Q axis (reactive power axis), expressed in units (pu).

The internal circuit performs a 68 ° lag phase shift on the voltage signal, so that the relay has the highest sensitivity when the system power factor angle θ=-90 ° (pure reactive power absorption). The action equation can be expressed as:

Panel setting value=VAB ⋅ IB3 ⋅ sin (8 ∘− θ) cos8 ∘

Panel setting value=3V AB ⋅ I B ⋅ cos8 ∘ sin (8 ∘− θ)

This design ensures that the relay can accurately respond to reactive power changes during demagnetization, while being insensitive to changes in active power, avoiding misoperation caused by load fluctuations.

2. Model code interpretation and key selection points

The model code of BE1-40Q consists of multiple characters, defining options such as current/voltage input mode, output contact form, timing characteristics, power type, target indication, and housing. Taking the example model F3E-E1P-B1S2F as an example:

F: The current input is 60Hz single-phase (CT secondary 5A), with other frequency and three-phase options available.

3: The voltage input is 120 Vac line voltage, corresponding to PT secondary 120V; there are also options such as 208V, 240V, etc.

E: The main output is a normally open (NO) contact.

E1: The timing feature is a definite time, and the delay is set by dialing the panel code.

P: The control power supply is in the range of 125Vdc/120Vac, and there are also 48Vdc, 24Vdc, 250Vdc/240Vac, etc.

B: An internal motivational goal indicator.

1: Equipped with a 'Push Test' button.

S: Equipped with power status output contacts (normally closed).

2: The auxiliary output is a normally closed (NC) contact.

F: Semi embedded installation shell.

Selection precautions:

The voltage input level must be consistent with the on-site PT secondary line voltage (120/208/240V).

The rated current input is 5A, and the CT transformation ratio needs to be coordinated with the setting calculation.

If a current type target indicator is required, the main output must be normally open (NO) because the current type target needs to be connected in series in the trip circuit, and normally closed contacts cannot provide a disconnected current path.

Choose between auxiliary output and power status output. If remote signal is required, select auxiliary output. If power monitoring is required, select power status output.

3. Installation wiring and grounding specifications

BE1-40Q adopts S1 standard chassis, which can be semi embedded or protruding installed, and does not require vertical installation due to its solid-state design. The installation dimensions and panel opening diagram can be found in Chapter 4 of the manual. The opening dimensions must be precise to ensure panel sealing.

Key points of electrical wiring:

Voltage input: Connect the line voltage V_AB to the designated terminals (such as terminals 6 and 7). The voltage circuit must be protected by fuses or miniature circuit breakers of the rated voltage level.

Current input: Connect the CT secondary circuit to the current input terminal, pay attention to polarity. The internal CT of the relay has an automatic short-circuit function - when the connecting plug is pulled out, the CT input terminal automatically shorts, avoiding the danger of CT open circuit.

Control power supply: Connect DC or AC power to the power terminals (such as terminals 3 and 4), without polarity requirements, but ensure that the voltage is within the allowable range (such as at least 14V for 24Vdc startup, and can be maintained as low as 12V).

Output contacts: The main output is used for tripping, and the auxiliary output is used for signaling. The wire diameter shall not be less than 14 AWG.

Grounding: The grounding terminal of the shell must be connected to the grounding grid with a copper wire of not less than 12 AWG, and independent leads are recommended.

EMI suppression: If the output contact drives the external relay coil, it is recommended to parallel reverse diodes (DC) or impedance capacitance absorption circuits (AC) at both ends of the coil to suppress electromagnetic interference when the contact is disconnected.

Insulation test warning: Before conducting a withstand voltage test, the connecting plug must be unplugged and the relay must be removed from the chassis, otherwise high voltage may damage the internal electronic components.

4. Setting calculation method and examples

The setting basis for BE1-40Q is the Capability Curve and static stability limit provided by the generator manufacturer. The setting goal is to place an 8 ° diagonal line below the intersection point of the capacity curve and the static stability limit, and calculate the intersection point value of the line with the Q axis as a unit, and then convert it into the specific gear of the panel TAP switch.

Setting steps (example):

Known: The rated apparent power of the generator is 100 MVA, the rated line voltage is 12.8 kV, the CT ratio is 5000/5, and the PT ratio is 12800/120.

Determine the minimum allowable reactive power absorption for demagnetization protection based on the capacity curve, assuming it is 0.4 pu of rated power (i.e. the three-phase transformer absorbs 40 Mvar).

Single phase reactive power=40/3=13.33 Mvar.

Convert the corresponding single-phase current: I=(single-phase reactive power × √ 3)/line voltage=(13.33 × 10 ^ 6 × 1.732)/12800 ≈ 1804 A (primary value).

Converted to CT secondary: Isec=1804/(5000/5)=1.804 A.

If the relay voltage is 120V (PT secondary), the required setting value (single-phase var) is (V_relay/√ 3) × I2/sec=(120/1.732) × 1.804 ≈ 125 var.

Refer to Table 1-1 (120V range LOW gear), 125 var corresponds to TAP position E (LOW gear, E is 125 var). If HI mode is selected, it corresponds to different ranges, but LOW mode meets the requirements here.

In practical engineering, a margin should be left for the setting value, usually taking 90% to 95% of the calculated value, to ensure reliable operation before the static stability limit. At the same time, it is necessary to consider the errors of PT/CT and the normal reactive power fluctuations of the system.

5. Panel operation and parameter setting

Main controls of BE1-40Q panel:

RANGE switch: HI/LOW two levels, switch internal CT ratio, and use TAP switch to achieve wide range setting.

TAP switch: 10 gears (A~K), corresponding to different var values. Specific values can be found on the panel label or in Table 1-1 of the manual.

TIME DELAY DIP: Two decimal digits, set to 0.1-9.9 seconds, with a step size of 0.1 seconds. If set to 00, it is an instantaneous action (<50ms).

Target reset button: Manually reset the target indicator that has been activated.

Output test button: Press with a non-conductive rod to manually excite the output relay for circuit verification.

Setting process:

Determine the TAP value and RANGE gear based on the tuning calculation.

Set a delay according to the system's requirements for time limits (such as setting the generator to 0.5-2.0 seconds to avoid system oscillation and external fault transients).

If instantaneous action is required, set the delay code to 00.

6. On site testing and verification methods

Before production or during regular calibration, it is necessary to conduct action value and delay tests on the relay. The following steps are based on the recommended test circuit in the manual (Figure 5-2).

6.1 Action value (Pickup) verification

Test circuit: The voltage source is connected to the voltage input terminal of the relay, and the current source is connected to the current input terminal, with adjustable phase between the two.

Set RANGE=LOW, TAP=A (minimum value), and set the delay to 10 (1.0s) to prevent frequent actions.

Apply rated voltage (120V/208V/240V depending on the model), adjust the phase of the current source to lag by 60 ° (simulate reactive power absorption).

Slowly increase the current until the PICKUP LED lights up, and record the effective voltage and current values at this time.

Calculate the actual single-phase var=(V/√ 3) × I, and compare it with the nominal value of the TAP gear in Table 1-1. The error should be within ± 2% or ± 0.1 var.

Test each TAP and HI gear in sequence, and record all points.

6.2 Delay characteristic verification

Using the same wiring, set TAP to A and delay to 11 (1.1s), 55 (5.5s), and 99 (9.9s), respectively.

The current jumps from zero to twice the operating current of the TAP gear (refer to Table 5-2 in the manual).

Measure the time from current application to output contact displacement with a timer, which should match the set value with an error within ± 5% or ± 50ms (whichever is greater).

6.3 Verification of Action Characteristic Curve (optional)

For situations where the entire 8 ° diagonal line needs to be verified, the operating current can be measured at different current phase angles (simulating different power factors), the corresponding P and Q can be calculated, and plotted on the complex power plane to verify whether it matches the theoretical 8 ° straight line. This method is suitable for laboratory calibration or fault analysis.

6.4 Output Circuit and Target Verification

Use the "Output Test" button to manually excite the output relay, observe whether the main and auxiliary contacts have shifted, and whether the target indicator is lit (if it is a current type, ensure that the tripping circuit has a current of at least 200mA).

Test power status output: Disconnect the control power supply, confirm that the status contacts are closed (normally closed), and open the contacts after restoring the power supply.

7. Maintenance and Storage Suggestions

BE1-40Q is a solid-state relay with simple daily maintenance, requiring only regular (recommended annual) functional testing. If stored for a long time as a spare part, it should be powered on for 30 minutes every year to maintain the performance of the internal aluminum electrolytic capacitor and extend its service life. If a malfunction occurs, do not disassemble or repair it on site. Instead, contact the manufacturer's technical support.