Yes, of course, short circuit calculations vary with power factor and voltage. For the three-phase system power factor is considered for short circuit calculation. Indeed, the Power factor is not the major concern in the single-phase short circuit current calculations. In an AC circuit, the power factor (PF) is a phase difference between voltage and current.
Short circuit current is an over current than rated current in any specific portion. If a short circuit occurs, then the voltage level and PF come to near zero and excessive heat occurs in the short circuit area. For this reason, different losses occur and the entire HVAC transmission system becomes inefficient.
What Is the Power Factor for Short Circuit Load?
Power factor comes to almost zero lagging with short circuit load condition and load becomes purely inductive load. Power factor plays a crucial role in the electrical power system. Short circuit current is inversely proportional to the power factor (PF). It means the power factor is massively reduced with a massively increasing short circuit current. PF becomes higher if the short circuit current becomes lower.
If PF is reduced, then what happens in the electrical power system? Frequency becomes lower with decreasing PF, system loss increases, voltage drop occurs, etc. So, PF should remain standard for reducing system loss, voltage drop, and frequency. Let’s see an equation
Where,
PF is the power factor.
Preal is the real power (in watts W).
Sapparent is the apparent power (in volt-amperes VA).
Do Short Circuit Calculations Vary with Power Factor and Voltage?
Yes, in a short circuit condition, the power factor becomes approximately zero (0) from one (1). Voltage is also reduced. We know that current is inversely proportional to voltage and vice versa. How is the power factor affected by the short circuit current? Let’s see with a simple example.
Indeed, the short circuit current depends on the total system impedance. Power factor affects the impedance of the system. This impedance is composed of resistance (R) and reactance (X). The power factor is related to these components.
Short Circuit Current Formula Isc:
Where,
Isc = Short circuit current.
V = System Voltage
Ztotal = Total impedance.
Total Impedance:
Where,
R = Resistance.
X = Reactance.
The relation between Power Factor and Impedance:
What is the formula for short circuit current and power factor? Power factor (PF) is related to the impedance angle (θ), and it’s expressed as
PF = Cos θ
It is noted that θ is the phase difference between voltage and current. The power factor is related to the ratio of resistance R to the total impedance Ztotal.
Short Circuit Current with Power Factor.
Now, substitute this equation for Ztotal into the short circuit current formula.
This equation shows that the short circuit current decreases as the power factor increases, and vice versa. So, if you have a question does the short circuit current increase with the power factor? No, a higher power factor is close to one (1) which means low reactance and more real power. It is noted due to high reactance, the power factor becomes very low in a short circuit condition.
Short-Circuit Current Calculations Process
A short circuit current is an excessive and uncontrolled current whose limit is higher than the rated current. Wherever a short circuit occurs then the medium becomes overheated. In that case, voltage and PF become very low, and the entire system loss increases.
However, how to calculate short circuit current? Let’s see a single-phase short circuit calculation system using a short circuit current calculation formula. To calculate current, voltage, and resistance we use Ohm law or short circuit impedance formula: V = IR
For finding current = I = V/R
For finding resistance = R = I/V
Single-Phase Short Circuits Calculation
The single-phase short circuit current calculation formula is Isc = Vsystem / Ztotal (where Z is an impedance).
Here,
Isc = Short-circuit current (in amperes)
Vsystem = System voltage at the fault location.
Ztotal = Total impedance (in ohms).
Three-Phase Short Circuits Calculation
To calculate 3 3-phase short circuit current, you have to apply the same formula as single-phase short circuit calculation. In that case, you have to add three three-phase systems. So, let’s see the 3-phase short circuit current calculation formula. This three-phase fault calculation formula illustrates short circuit current, line voltage, three-phase, and total impedance.
Here,
Isc = Three-phase short-circuit current (in amperes).
VLL = Line-to-line system voltage (in volts).
Ztotal = Total impedance to the fault (in ohms).
Voltage Drop Calculation Process
In any system, if the voltage limit becomes lower than the rated voltage level for a specific time it is called a Voltage drop. Voltage drop occurs due to high current or impedance. In most cases, a voltage drop occurs in the longer power lines due to higher resistance, and lower cross-sectional area. However, let’s see a voltage drop calculation formula. This formula will assist you in calculating the voltage drop of the cable due to its resistance and reactance.
Vdrop = I * (R.L + X.L)
For resistive circuit
Vdrop = I * R * L
Here,
Vdrop = Voltage drop (in volts).
I = Current (in amperes).
R = Resistance of the conductor (in ohms per unit length).
X = Reactance of the conductor (in ohms per unit length).
L = Length of the conductor.
For Copper Conductors
Copper is a well-standard conductive material used in power systems. Voltage drop occurs in copper conductors due to the material’s inherent resistance. Higher resistance lowers the voltage limit. In most cases, a voltage drop occurs in a copper conductor due to resistance. However, to calculate copper conductor voltage drop use this formula.
Vdrop = 2 * I * L * R / 1000
Suppose, 10 American Wire Gauge AWG) copper wire run 100-meter length (L) and carry 20 amps (I). In that case a resistance of 3.277 ohms (R) per kilometer.
Now Vdrop = 2 * 20 * 100 * 3.277/1000 = 13.11volts
This means that the voltage drop across the copper conductor would be 13.11V.
For aluminum conductors, how would you calculate the voltage drop of aluminum conductors? Very simple to follow the above section (copper conductor voltage drop calculation process) and find the aluminum conductor voltage drop.
How Does the Power Factor Change in The Process of Short Circuit Characterization?
The power factor is the phase angle between voltage and current. PF is directly proportional to the voltage but inversely proportional to the current. However, in a short circuit characterization, the PF limit comes to near about zero (0). The standard power factor (PF) is considered from 0.95 to 1 and 0.95 to 0.85 is poor or normal.
If the power factor comes below 0.85 then it is considered as the low power factor. During the fault condition, PF comes in a lower stage like 0.70, 0.50, 0.35, 0.10, and so on. In that case, some essential factor happens, and let’s see a low power factor impact examples such as
- Copper loss becomes higher (I2R).
- Voltage drop occurs in transmission line, transformer, etc.
- Low-frequency level below (50 Hz).
- Increase entire system cost.
- The entire system becomes inefficient.
To avoid the above essential things, we must improve the power factor and remove short circuits. So, short circuits really harm our entire power system.
Does Voltage Affect Short Circuit?
Indeed, in an electrical power system, short circuit current affects the transmission line voltage or system voltage. Suppose, a short circuit has occurred at an electrical substation in that case, the short circuit area will be overheated and the current limit will be more excessive than the normal value.
In that case, the voltage will come to a low value. It means voltage will be dropped drastically. It is noted that the constant resistance, the voltage increase with increasing current limit. Sometimes it happens in healthy conditions.
Which Areas of the Power Distribution System Are Critical for Short Circuit Calculations?
A short circuit is a common event in the HVAC system or LVAC system. Different types of short circuits occur in the power system such as line-to-line faults, single-line-to-ground faults, double-line-to-ground faults, three-phase faults, earth faults, and others. In a power distribution system, different types of devices are installed. These are very expensive and sometimes short circuits occur in such devices.
- Electrical Power Transformers.
- High voltage Circuit Breakers.
- High voltage Transmission line.
- Electrical Substations.
- Bus bar.
- Switchgear.
- AC generator.
- Protective Relays.
- Distribution Panels.
Can I Use a Short Circuit Current Calculator for Short Circuit Calculation?
Yes, why not? You can use a short-circuit current calculator for short-circuit current calculations. A short circuit calculator is a tool. It was designed to help engineers and electricians find the short-circuit current quickly depending on the command. However, three main parameters can be provided to this calculator such as
- The voltage level of the system.
- Impedance of transformers, cables, and other equipment.
- Distance between the source and the fault point.
After providing such information, you can see the result on the display. However, there are available fault current calculators. You can find the best calculator and calculate. So, the calculation of fault current in the power system is simple. So, stay safe and make your power line safe from unexpected short circuit conditions.
Final Thought
We have found the answer do Short Circuit Calculations Vary with Power Factor and Voltage? Yes, but for the single-phase AC system power factor is negligible. In a three-phase system power factor plays a major role in short circuit calculation. Voltage is always with a short circuit calculation system. This is because voltage and current both are important parts of the power system but they are inversely proportional. I have shown short circuit calculations with power factor and voltage, I have also referred to different terms and formulas that are crucial to know.