Electrical Formula's
1. Ohm’s Law:
Ohm’s Law states that Voltage (V) = Current (I) × Resistance (R). Where V is voltage in volts, I is current in amperes, and R is resistance in ohms. It explains the relationship between electrical parameters in a circuit.
2. Power Formulas:
DC Power: P=V×I; where Power is the product of voltage (V) and current (I).
Single Phase AC Power: P=V × I × Cosϕ
Three Phase AC Power: P=1.732 × V × I × Cosϕ
3. Energy Consumption: E=P × t
E = Energy (kWh); P = Power (kW) & t = Time (Hours)
4. Power Factor:
Power Factor is calculated as KW ÷ KVA
Which shows how efficiently electrical power is being used. It's value ranges from 0 to 1, and it can be lagging (inductive load) or leading (capacitive load). A higher power factor indicates better efficiency and reduced energy losses.
5. Conversion between: KVA ↔ kW:
To convert KVA to KW:
KW = KVA × Cosϕ, where cosϕ is the power factor.
To convert kW to kVA:
KVA = KW ÷ Cosϕ.
These formulas help in understanding real and apparent power in electrical systems.
6. Conversion between: KW ↔ Amps
Single Phase: I=kW/(1000xV×cosϕ)
Three Phase: I=kW/(1000x1.732×V×cosϕ)
These formulas help calculate current based on power, voltage, and power factor in electrical systems.
7. Conversion between: KVA ↔ Amps
Single Phase: I=kVA/(1000xV)
Three Phase: I=kVA/(1000x1.732×V)
These formulas help determine current based on apparent power and voltage in electrical systems.
8. Conversion between: HP ↔ KW
KW=HP×0.746
This means that one horsepower is equal to 0.746 kilowatts. For example, if you have a motor rated at 10 HP, its power in kilowatts would be 10 × 0.746 = 7.46 kW.
HP=KW/0.746
In other words, you can find the equivalent horsepower by dividing the power in kilowatts by 0.746. For instance, if a machine has a power rating of 15 kW, its horsepower would be 15 / 0.746 ≈ 20.13 HP.
These formulas are commonly used in electrical and mechanical engineering to convert between the two units of power, depending on the requirements of the application.
9. Full Load Current Calculation from kVA Rating (3-Phase):
For a Transformer (3-Phase): I=kVA/(1000x1.732×V)
DG Set (3-Phase): I=kVA/(1000x1.732×V)
These formula helps you determine the maximum current that the DG/transformer set can supply at its rated kVA and voltage. Here-
I is the full load current in amperes (A),
KVA is the apparent power rating of the transformer in kilovolt-amperes,
V is the line-to-line voltage in volts (V),
1.732 is the square root of 3, which is used for three-phase calculations.
10. Transformer Turns Ratio:
V2/V1=N2/N1 = I1/I2; where:
V1,V2 = Primary & Secondary Voltages
N1,N2 = Number of Turns in Primary & Secondary
11. Efficiency: η=Output Power/Input Power×100%
12. Resistance of a Conductor
R=ρ×LAR=ρ×AL
ρ = Resistivity; L = Length & A = Cross-sectional Area
13. Inductive Reactance
Inductive reactance, denoted by XL, is the opposition that an inductor offers to the flow of alternating current (AC) due to its inductance. It is calculated using the following formula:
XL=2πfL
This formula shows that the inductive reactance increases with both the frequency of the supply and the value of the inductance. In other words, as either the frequency or the inductance increases, the opposition to the AC current also increases. Where:
XL is the inductive reactance measured in ohms (Ω),
F is the frequency of the AC supply in hertz (Hz),
L is the inductance of the coil in Henries (H),
2π is a constant (approximately 6.283).
14. Capacitive Reactance
Capacitive reactance, represented by XC is the opposition that a capacitor offers to the flow of alternating current (AC) in a circuit. It is calculated using the following formula:
XC=1/ 2πfC
This formula shows that the capacitive reactance decreases as either the frequency or the capacitance increases. In other words, higher frequency or larger capacitance results in lower opposition to the flow of AC current through the capacitor. Where-
XC is the capacitive reactance measured in ohms (Ω),
F is the frequency of the AC supply in hertz (Hz),
C is the capacitance of the capacitor in farads (F),
2π is a constant (approximately 6.283).
15. Voltage Drop (Approximate)
The approximate voltage drop (VD) in a cable can be calculated using the following formula:
VD=(2×L×I×R)/1000
In this formula, L represents the one-way length of the cable and R is the resistance per kilometer, which depends on the type and size of the cable used.
This calculation helps in estimating the voltage loss that occurs due to the resistance of the cable when current flows through it, which is important for ensuring proper voltage at the load end.
16. Load Factor:
The Load factor is a measure of how efficiently electrical power is being used over a specific period of time. It is calculated using the following formula:
Load Factor=Average Load/Peak Load; Where:
Average Load is the average amount of electrical load (in kW or MW) consumed over a given period.
Peak Load is the maximum load demand recorded during the same period.
17. Demand Factor:
The demand factor is an important parameter used in electrical engineering to assess the actual utilization of the connected electrical load. It is calculated using the following formula:
Demand Factor=Maximum Demand / Connected Load
This factor helps in designing and sizing electrical systems more efficiently by considering the actual usage patterns. Where:
Maximum Demand is the highest level of electrical power demand recorded over a specific period.
Connected Load is the total rated capacity of all electrical equipment connected to the system.
18. Diversity Factor
The diversity factor is a key concept in electrical engineering, used to describe how the maximum demands of individual loads compare to the maximum demand of the entire system. It is calculated using the following formula:
Diversity Factor=Sum of Individual Max Demands/ Max Demand of Total System.
Sum of Individual Maximum Demands refers to the total of the highest demands recorded for each individual load or equipment.
Maximum Demand of Total System is the highest demand recorded for the entire electrical system as a whole.