CSC237B Motor Integrated Protection Measurement and Control Device

Beijing Sifang CSC237B Motor Comprehensive Protection and Control Device

1.1 Device Introduction

This device is suitable for various non-directly grounded neutral systems of 10kV and below, serving as comprehensive protection for large synchronous motors against phase-to-phase faults, overload, out-of-step protection, loss of excitation protection, and asynchronous impact protection. It can be installed locally in switchgear cabinets.

1.2 Main Functions

1.2.1 Protection Functions

„ Instantaneous overcurrent protection for phase-to-phase faults

„ Overcurrent protection for locked rotor conditions

„ Overload protection (trip or alarm signaling can be selected)

„ Long start protection

„ Overheating protection (overheating trip, overheating alarm, thermal accumulation memory function)

„ Unbalance protection (phase loss/reverse phase, negative sequence overcurrent protection, definite time or inverse time can be selected)

„ Ground protection (zero-sequence overcurrent protection, output can be set to trip or signal, definite time or inverse time can be selected)

„ Under-voltage protection

„ F-C overcurrent blocking

„ Non-electrical protection

„ Out-of-step protection

„ Loss of excitation protection

„ Asynchronous impact protection

1.2.2 Measurement and Control Functions

„ 15 channels of digital input for remote signaling collection, device remote signaling change, and accident remote signaling

„ Remote control of normal circuit breaker opening and closing

„ Remote measurement of analog quantities such as Ua, Ub, Uc, Ia, Ic, P, Q, COSф, etc.

„ Various event SOE, etc.

„ 4-20mA function

11.3 Protection Components

For the protection principles of overcurrent, overheating, unbalance, grounding, under-voltage, etc., please refer to the CSC-237A asynchronous motor protection and control device manual.

Note: The CSC237B instantaneous overcurrent protection does not include directional elements.

1.3.1 Out-of-Step Protection

During operation of a synchronous motor, if the excitation voltage or supply voltage decreases, the motor's driving torque will reduce. When the maximum torque is less than the braking torque of the mechanical load, the synchronous motor loses synchronism and oscillates relative to the system. The power angle difference between the motor's induced electromotive force and the power supply electromotive force varies periodically between 0° and 360°.

The out-of-step protection is automatically enabled after the motor starts. It operates with a time delay when the motor loses synchronism. For critical motors, it acts on the resynchronization control circuit. For motors that cannot or do not require resynchronization, it acts to trip. This protection has two output actions: one acts on the resynchronization control circuit, and the other acts to trip the circuit breaker and excitation switch.

The out-of-step protection is based on detecting the motor's power factor angle. Under normal operation, synchronous motors usually operate in an over-excited state, with a negative power factor angle ϕ M. When the synchronous motor loses synchronism, it must pass through an under-excited state, where ϕ M is positive. The protection operating zone is:

ϕ SET < ϕ M < 180° − ϕ SET

Where: ϕ SET is the set value of the power factor angle (generally 30°), and ϕ M is the actual measured power factor angle. This criterion requires that the measured power factor angles of all three phases, ϕ MAB, ϕ MBC, and ϕ MCA, all meet the condition to operate.

To prevent false operation during no-load conditions or other situations, a stator low-current blocking element is provided.

In addition to meeting the above conditions, an impedance condition must also be satisfied. When the impedance is outside the static stability impedance circle, the protection is blocked.