This demonstration illustrates fault and islanding of an induction motor/diesel-generator system and demonstrates the Machine Load Flow option of the Powergui. (See Chapter 2 of the User's Guide).

G. Sybille (Hydro-Quebec)

Contents

Circuit Description Demonstration

Circuit Description

1

A plant consisting of a resistive and motor load (ASM) is fed at 2400 V from a distibution 25 kV network through a 6 MVA 25/2 kV Wye-Delta transformer and from an emergency synchronous generator/ diesel engine unit (SM). The 25 kV network is modelled by a simple R-L equivalent source (short-circuit level 1000 MVA) and a 5 MW load. The asynchronous motor is rated 2250 HP, 2.4 kV and the synchronous machine is rated 3.125 MVA, 2.4kV. The SM excitation is performed by the standard excitation block provided in the machine library. The diesel engine and governor system are modelled by a Simulink® block (See tutorial, session 7 in the User`s Guide). Initially, the motor develops a mechanical power of 2000 HP (1.49 MW) and the diesel generator is in standby, providing no active power.The synchronous machine excitation system controls the 2400 V bus B2 voltage at 1 pu. At t = 0.1 s, a three-phase to ground fault occurs on the 25 kV system, causing opening of the 25kV circuit breaker at t = 0.2 s.

Một nhà máy gồm tải động cơ (ASM) được cấp 2400V từ một lưới phân phối 25kV thông qua MBA và từ MFĐ ĐB/Diesel (SM) khẩn cấp. Lưới 25kV được mô hình hóa bởi một nguồn R-L đơn giản (cấp ngắn mạch 1000MVA) và một tải 5MW.

ĐCKĐB định mức tại 2250 HP, 2.4kV và MFĐ ĐB định mức tại 3.125 MVA, 2.4kV. Kích từ SM được thực hiện bằng khối kích từ cơ bản. Ban đầu, motor tăng đến công suất cơ đêbs 2000HP (1.49MW) và MF Diesel ở trạng thái chờ, không cấp CS tác dụng. Hệ kích từ được điều khiển bởi điện áp 2400V trên bus B2 tại 1pu. Tại t = 0.1s, lỗi 3 pha nối đất xảy ra trên lưới 25kV, gây ra hở mạch lưới 25kV tại t = 0.2s.

The demonstration illustrates the mechanical and electrical transients following the fault and islanding of the Motor/Generator system.

Demonstration

1. Start Simulation. If the SM and ASM initial conditions are not properly set, you observe that the voltage and currents Machine do not start in steady state. Stop the simulation.

2. In order to start the simulation in steady-state, you must initialize the synchronous machine and the asynchronous motor for the desired load flow. Open the Powergui and select "Load Flow & Machine initialization" . The machine "Bus type" should be already initialized as "PV generator", indicating that the load flow will be performed with the machine controlling its active power and terminal voltage. Specify the desired values by entering the following parameters:

Load Flow : U AB (Vrms) = 2400 , P (Watts) = 0. Specify also the ASM mechanical power by entering Pmec (Watts) = 2000*746.

Then press the "Update Load Flow" button.

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Once the load flow is solved, the three line-to-line machine voltages and the three machine currents are updated. The SM reactive power, mechanical power and field voltage are displayed: Q = 856 kvar; Pmec = 844 W (power required by resistive losses in stator winding ); field voltage Ef = 1.4273 pu; the active and reactive powers absorbed by the motor, slip and torque are also displayed.

3. The diesel engine governor and SM excitation system contain integrators and transfer functions which have also been initialized by the load flow. Open the GOVERNOR block in the Diesel Engine subsystem. Note that the initial mechanical power has been automatically set to 0.00027 pu (844 W). Now open the EXCITATION block. Notice in the last line of the block menu, that the initial terminal voltage Vt0 and field voltage Vf0 have been set respectively to 1.0 and 1.4273 pu.The value of the constant block connected to the torque input of the asynchronous motor has also been automatically set to 7964 N.

4. Open the SM and ASM scopes displaying the synchronous machine and asynchronous machine signals. Start the simulation. Observe that during the fault the terminal voltage drops to about 0.2 pu and the excitation voltage hits the limit of 6 pu. After fault clearing and islanding the SM mechanical power increases from its initial value of 0 pu to the final value of 0.80 pu required by the resistive and motor load (2.49 MW). After 3 seconds, the terminal voltage stabilizes at 1 pu. The motor speed decreases transiently from 1789 rpm to 1635 rpm, then it recovers close to its normal value after 2 seconds.

If you increase the fault duration to 12 cycles by changing the breaker opening time to 0.3 s, you will notice that the system collapses. The ASM speed slows down to zero after 2 seconds.

3

Có D-STATCOM

4

Không có STATCOM

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