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.