Location

This example model can be found in the software under the category "Distribution and Industrial Power Systems" > "Diesel_Generator_with_25SYNC.ecf".

Description

The model consists of a 25 kV grid source powering a 5 MW load at the terminals. In addition, a 1 MW resistive load and 2250 HP asynchronous motor load are also connected through a 6 MVA, 25/2.4 kV transformer. A 3.125 MVA emergency Diesel Generator (DG) modeled through a synchronous generator and machine controls (Diesel governor – DEGOV1 and AC1A exciter) is connected to the secondary of the transformer feeding the asynchronous motor and resistive loads.

The model also consists of a three-phase main breaker at the transformer primary which isolates the network into two parts when a three-phase to ground fault occurs at the grid side. A 25 Synchronism-Check relay is used to synchronize the breaker closing after the fault clears.

Steps

To start the simulation in steady state, the synchronous machine and the asynchronous motor need to be initialized by the Load Flow.

The first step to run the simulation is to calculate the load flow. Since the model is running at 60 Hz, you have to make sure the frequency for load flow is also 60 Hz.

Step 1: Open Network -> Load Flow and make sure the frequency is 60 Hz. You don't have to execute load flow in this section.

Step 2: Open Simulation Settings and enable the option "Perform load flow and set initial conditions at simulation start". Make sure the time step is set to 50 us. Select your target and run the simulation.

Simulation and Results

Initially, the grid supplies power to all the loads and the emergency diesel generator is supplying zero power. A fault occurs close to the grid, thus opening the breaker and isolating the network into two parts – and the DG ramps up to power the loads connected to it. Upon fault clearing, the 25 Synchronism-Check relay issues the breaker close command when the difference values of voltage, frequency and phase angle (dV, df, dPhi) on either side of the breaker are within the specified threshold of 10%, 0.4Hz and 5 deg respectively. The DG power is ramped down to a minimum for a brief period and then switched off, thus resembling a typical industrial/commercial setup operation.

The following sequence of events demonstrate the working of the 25 Synchronism-Check relay and DG working. The sequence of events are applied by loading "Diesel_Generator_with_25SYNC.svt" in ScopeView and starting a data acquisition with Sync and Trigger options checked:

• Perform the load flow and set the initial values before starting the simulation.
• At t = 0.8 s, LLL-G fault occurs.
• At t = 1 s, Circuit Breaker (CB) 1 opens. Grid side frequency increases to 60.2Hz.
• At t = 1.2 s, fault clears.
• At t = 4 s, 25 Synchronism-Check relay becomes operational.
• At t = 6 s, Grid side frequency restores to 60 Hz.
• At t = 6.58 s, 25 Synchronism-Check Relay issues the close command to CB1.
• At t = 9 s, DG power is reduced to 10 %.
• At t = 11 s, Load of 100 kW at Bus 3 is switched On.
• At t = 14 s, Load of 100 kW at Bus 3 is switched Off.
• At t = 15 s, DG power is reduced to 0.

Synchronous machine control response is shown in below figure:

Bus voltages are shown in below figures:

Zoom in voltages:

Figure below shows the performance of 25- Synchronism-Check relay. The 25Sync relay issues a close command when the dV, df and dPhi are within the specified threshold. Accordingly, it can be seen though the grid is back at 6s, the breaker close command is issued at 6.58s when the parameters are within the threshold of 10%, 0.4Hz and 5 deg respectively.

25kV grid side circuit breaker status is shown below:

Note: Circuit Breaker status

• 1- Close
• 0 - Open

Reference

1. Emergency Diesel-Generator and Asynchronous Motor- https://www.mathworks.com/help/physmod/sps/examples/emergency-diesel-generator-and-asynchronous-motor.html