Saving the electrical power system in stable condition is considered as one of important challenges to avoid any failure of high voltage equipment. Additionally, with the increasing off the critical loads , it’s very important to use the accurate protection system that can deal with any abnormal condition. This paper stud ies one of critical cases that can effect on the coordination of the protection system with the faults during fuse fail condition. Over Head transmission line (OHTL) is the most part in the power system that faces the disturbances, which can be protected by multi-protection functions as line differential function, distance protection function, over current, earth fault, over/under voltage etc. The distance protection function is depending on the line voltage and the load current to calculate the load zone. This paper aims to prevent the falls operation of distance protection function during voltage transformer fuse failure condition.
With the population growth and the increase of the life standers, the electrical power system has been extended to absorb the required demand power. Besides, the electrical power system became more complex, which leads to classifying the power system to distribution, transmission, and generation to be easy for controlling and saving the reliable and stable system [
There are some abnormal conditions in the power system, that can lead to the loss of synchronism between the generation and the load, for example at isolating high-loads from the system, at tripping of one of the generation systems, and at these cases, the mechanical power is not equalized with the required for the electrical loads [
to adjust the distance protection tripping time to operate instantaneously by zero-time delay for 100% of the protected transmission line, also the errors can shift the out of zone fault to the protected area. Hence, the distance protection instantaneous trip is typically set to cover 80% from OHTL which is called the first zone, and the remaining 20% of OHTL can be covered by the time delay of the second zone trip, where the second zone is covered 100% of OHTL and between 20% to 50% of the next small OHTL. In another hand, by assuming the voltage source is failed through a voltage fuse fail, the base operation of the distance protection function will calculate the load impedance as a very low value which will cause a false trip command to the transmission line. Digital technology provides guarantee for the smoothness of network information. Under the premise of ensuring the intelligentization of equipment, the advantages of network information application are given full play to unify the control of the distribution device in the substation system. Primary intelligence and secondary network are the most significant characteristics of smart substation [
To analyze the fault, it’s important to simulate the fault in three components that’s positive sequence and negative sequence and zero sequences, as shown in the below
Firstly, the Change in magnitude:
a = 1 ∠ 120 ˚ (1)
a 2 = 1 ∠ 240 ˚ (2)
a 3 = 1 ∠ 360 ˚ (3)
From these equations, useful combinations can arrive
1 − a = 3 ∠ − 30 ˚
a 2 − a = 3 ∠ 270 ˚ (4)
Or
1 + a + a 2 = 0
1 − a 2 = 3 ∠ 30 ˚ (5)
Or
a − a 2 = 3 ∠ 90 ˚ (6)
Any three-phase system of phasors will always be the sum of the three components.
“+VE” sequence: V a 1 V b 1 V c 1
“−VE” sequence: V a 2 V b 2 V c 2
“0” sequence: V a 0 V b 0 V c 0
The original system phase components can be presented from Va, Vb and Vc
[ V a = V a 0 + V a 1 + V a 2 V b = V b 0 + V b 1 + V b 2 V c = V c 0 + V c 1 + V c 2 ] (7)
From Equations (1) to (5) Zero sequence component
V a 0 = V b 0 = V c 0
Positive sequence component
V b 1 = a 2 V a 1 , V c 1 = a V a 1
Negative sequence component
V b 2 = a V a 2 , V c 2 = a 2 V a 2
Va, Vb and Vc can be expressed in terms of phase “a” component only as:
V a = V a 0 + V a 1 + V a 2
V b = V a 0 + a 2 V a 1 + a V a 2
V c = V a 0 + a V a 1 + a 2 V a 2
This equation can be accomplished in a matrix form:
[ V a V b V c ] = [ 1 1 1 1 a 2 a 1 a a 2 ] [ V a 0 V a 1 V a 2 ] (8)
Equation (8) can be written as:
A = [ 1 1 1 1 a 2 a 1 a a 2 ] , [ V a V b V c ] = A [ V a 0 V a 1 V a 2 ]
This equation can be reversed in order to obtain the positive, negative and zero sequences from the system phasors.
[ V a 0 V a 1 V a 2 ] = A − 1 [ V a V b V c ] (9)
With considering,
A − 1 = 1 3 [ 1 1 1 1 a a 2 1 a 2 a ]
OHTL has an impedance per kilometer related to its design and construction which will be a function of OHTL length. The distance protection function looks at load current and the grid voltage, that use these values for impedance calculation related to Ohm’s law. Conventional time-stepped distance protection is illustrated in
It’s not practical to design the distance protection that can operate during the non-fault condition regarding the failure of feed the voltage to the measurement unit, that will consider the calculation in the protected zone. Using the fuse fail functional to block the distance protection is very important to prevent the false
operation of the distance protection function. The proposed solution in this paper is presented in three ways to block the distance function as shown in the below
It’s very important to protect the voltage transformer from the short circuit. The short circuit will consume a very high current which direct will damage the voltage transformer secondary coil. That can protect by fuses or Miniature Circuit Breaker (MCB). So, by using an auxiliary contact from the secondary connection from the miniature circuit breaker to be used as a binary input to the distance for block the function.
This way is depending on the fuse fail relay that can feed on both winding in the line voltage transformer to compare both measuring coils with using the binary output from the fuse fail relay to be used a binary input for blocking the distance protection relay as shown in
In the numerical distance protection relay, it’s possible to use the internal fuse fail function which depends on the changing in the voltage and currents, as shown in
The proposed analysis in this part has been validated with the protection numerical relays to shows the test result created by the secondary injection kit
software to simulate the distance protection function during symmetrical fault analysis. Also, this part simulates the distance blocking during VT fuse fail.
The simulated experiment in this paper used by a secondary injection kit, the operating voltage for the simulated system is 115 kV, the voltage transformer ratio is (115 kV/115V) and the current transformer ratio is (1200 A/1A) [
distance protection symmetrical fault which discusses the boundaries results in
The simulation of VT fuse fail can be implemented by normal load injection to the protection distance relay, with applying setting of VT MCB trip after healthy condition. The below
Rapidly growing electricity demand deregulated electricity market systems, and restructured operation of power delivery systems are stressed the power grid operation. In such a situation, the speed of fault clearance is very important to
| NO | R (Ω) | X (Ω) | Z (Ω) | Z phi | Zones |
|---|---|---|---|---|---|
| 1 | 0.000 | 2.024 | 2.024 | 90.0 | 1 |
| 2 | 0.000 | 4.357 | 4.357 | 90.0 | 2 |
| 3 | 0.000 | 5.761 | 5.761 | 90.0 | 4 |
| 4 | −0.823 | 2.023 | 2.184 | 112.2 | 1 |
| 5 | −1.779 | 4.370 | 4.719 | 112.2 | 2 |
| 6 | −2.076 | 5.099 | 5.506 | 112.2 | 4 |
| 7 | 0.000 | −4.331 | 4.332 | 270.0 | 3 |
| 8 | 0.170 | 2.022 | 2.029 | 85.2 | 1 |
| 9 | 0.363 | 4.314 | 4.329 | 85.2 | 2 |
| 10 | 0.487 | 5.795 | 5.815 | 85.2 | 4 |
| 11 | 0.671 | 1.994 | 2.103 | 71.5 | 1 |
| 12 | 1.464 | 4.354 | 4.594 | 71.5 | 2 |
| 13 | 1.935 | 5.756 | 6.072 | 71.5 | 4 |
| 14 | 1.278 | −4.315 | 4.501 | 286.5 | 3 |
| 15 | −1.237 | −4.360 | 4.533 | 254.2 | 3 |
| NO | R (Ω) | X (Ω) | Z (Ω) | Z phi | Setting Time - Second | Trip Time - Second | Zone |
|---|---|---|---|---|---|---|---|
| 1 | −1.328 | 5.314 | 5.478 | 104.1 | 1.200 | 1.224 | 4 |
| 2 | −1.200 | 3.771 | 3.958 | 107.7 | 0.400 | 0.423 | 2 |
| 3 | 0.300 | 1.286 | 1.321 | 76.9 | 50.00 | 0.027 | 1 |
| 4 | 0.514 | 3.214 | 3.255 | 81.0 | 0.400 | 0.425 | 2 |
| 5 | 1.071 | 3.857 | 4.003 | 74.5 | 0.400 | 0.426 | 2 |
| 6 | 0.685 | 5.571 | 5.613 | 83.0 | 1.200 | 1.226 | 4 |
| 7 | −0.428 | 1.542 | 1.601 | 105.6 | 50.00 | 0.024 | 1 |
| 8 | 0.985 | 2.142 | 2.358 | 65.4 | 0.400 | 0.425 | 2 |
| 9 | −0.771 | −1.371 | 1.573 | 240.7 | 0.800 | 0.829 | 3 |
| 10 | 0.685 | −2.142 | 2.249 | 287.8 | 0.800 | 0.827 | 3 |
| 11 | −0.300 | −3.471 | 3.484 | 265.1 | 0.800 | 0.829 | 3 |
| Zone No | With VT fail | Without VT fail |
|---|---|---|
| 1 Forward | Blocked | 23.0 msec |
| 2 Forward | Blocked | 439 msec |
| 3 Reverse | Blocked | 830 msec |
| 4 Forward | Blocked | 1.0 Sec |
maintain the system stability. Distance protection primarily uses two zones of protection to cover protection for the entire line distance. Typically, zone-1 covers 80% of the protected line length and operates instantaneously and Zone-2 is set to be an intentional overreaching zone to cover the 100% protected line. Zone-2 operates with a predefined time delay of about 15 - 20 cycles (300 - 400 ms). But it’s not correct to design the distance protection that can operate during the non-fault condition regarding the failure of feeding the voltage to the measurement unit, which will consider the calculation in the protected zone. Using the fuse fail to function to block the distance protection is very important to prevent the false operation of the distance protection function. The proposed solution in this paper is presented in three ways. The first presented way is using an auxiliary contact from the secondary connection from the miniature circuit breaker to be used as a binary input to the distance for block the function. The second presented way is depending on the fuse fail relay that can feed from both winding in the line voltage transformer to compare both measuring coils with using the binary output from the fuse fail relay to be used a binary input for blocking the distance protection relay. The third way is depending on the internal fuse failing to function in the distance relay for blocking the distance relay.
The authors declare no conflicts of interest regarding the publication of this paper.
Eltamaly, A.M. and Elghaffar, A.N.A. (2022) A Smart Strategy for Blocking the Distance Protection Function during VT Fuse Failure. Intelligent Control and Automation, 13, 25-37. https://doi.org/10.4236/ica.2022.133003