Calculating fault location from COMTRADE file through Wavewin

Introduction: Basic information regarding COMTRADE files (CFG and DAT) was given in earlier post here: Understanding disturbance record files. It is recommended to read this first.

Fault location is and important information, which is provided by fault locator installed for feeders. Normally it is inbuilt feature distance protection. Fault locator has record for latest faults locations (No. of records vary depending on Make/Model of device). Or there may be cases where we have COMTRADE files but access to device records is not available. In these cases we may calculate location from COMTRADE file.

Procedure: 

Open the file with Wavewin software. For fault location calculation, Clicke on Data > Fault Detector, A new window is opened as below

In the DR file, it can be seen that although Secondary is shown on the title bar, current and voltage values are in primary values (Voltage =241646V and Current =219A). This is because CT / VT ratio data is not available in this CFG / DAT file. It is taken as 1:1. It can be checked as below:

The information whether the CT and VT ratio is available or not, is an important information. We have to enter line parameters in Primary or Secondary based on it. In this example Secondary values are equal to Primary values of voltage and current (Due to 1:1 CT and VT ratio). Therefore we will enter primary side line parameters as per relay setting data: 

Positive sequence impedance Z1 = 0.301 ohm/km
Line angle = 80 deg
Zeo sequence compensation factor kZn = 0.750 
kZn angle = -10 deg
Line Length = 100km

In case of actual CT and VT ratio is available in disturbance record files, secondary parameters are to be entered.

Click here for more detail on line parameters

We can specify faulted phase in Advanced settings, which we have not used. Software has automatically sensed faulty phase and shown fault location.

Trip Circuit Supervision

Introduction: Trip circuit supervision relays (TSR) are used for monitoring of healthiness of Circuit Breaker trip circuit. During any fault in Power system, circuit breakers have to interrupt the fault currents. But if trip circuit is not healthy CB will not operate and fault will not be cleared. This will lead to operation of Breaker Failure Protection, causing larger disturbance in Power system and major damage to equipment. Click here for more information on Breaker Failure Protection (BFP).

Post close supervision: When the system is normal working condition the CB will be in closed state. In case any fault is detected by protection relays, it issue tripping command to CB. Trip circuit should be healthy so that CB is tripped without any failure.

Pre close supervision: When the CB is being closed from open state, the voltage will extend to uncharged portion. There may be existing fault in the system being charged which will lead to operation of protection relay. The CB trip circuit should be in healthy state so that any fault is cleared without ant delay.

The typical schematic is shown here

TSR relay is connected in series with trip coil. Trip coil is high energy coil (Low resistance, high current), due to fast operation required for CB. TSR relay is low energy coil (High resistance, low current). 

For example, resistance of CB trip coild is 55 ohm, operating voltage is 110V. Pickup current for CB tripping is 2A. TSR relay has resistance of 1100 ohm. Its pickup current will be low 100mA. All the relays are designed for pickup up at 60-70% os rated voltage / current. Therefore TSR will pickup at ~70mA).

As shown above, during normal condition when CB is close, both coils will be in series. Current through TSR will be 95mA. When tripping command is issued to CB, Post-close TSR will get bypassed. In this case, after CB is opened 52a will open and 52b will close. Now, post-close TSR will get de-energised and pre-close TSR will be energised. 

if any one relay (pre-close / post-close) is energised TSR alarm relay should be in energised condition. If both (pre-close and post-close) relays are de-energised TSR alarm relay gets denergised and alarm is generated to operator. A time delay of ~200ms is given to avoid false alarm during CB close / open operation.