What is a Single-phase AC circuit?

Alternating Current (AC) is a type of electric power in which the electric current changes, both in magnitude and direction, at regular intervals. This AC Circuits can deliver power in either a Single Phase system or a Three Phase system.

A single-phase system, circuit, or device has, produces, or uses a single alternating voltage source. In electrical engineering, single-phase voltage source power refers to the distribution of electricity using a system in which all supply voltages vary simultaneously.

Single-phase power supply

Single-phase voltage power is a two-wire (AC) power switch. It consist of a single power wire called a phase wire, and a single neutral wire.

Generally, a single-phase current is called a “residential voltage” because it is widely used in homes. When it comes to average power transmission, a single-phase power supply connection uses both neutral wire and phase supply cables. A single-phase power is used when electricity demand is low. In short, it is for the use of small machines. Three-phase power carries a heavy load and can operate large machinery in factories.

In a single-phase power connection, the split-phase voltage starts at 230 Volts Amperes and has a frequency of about 50 Hertz. As the high voltage source across the single-phase voltage connection increases and decreases steadily, continuous power is not delivered to the load.

AC circuit

Current Switch Circuits or AC circuits are powered by Switch Source, either current or voltage. Alternating Voltage or Current is where a voltage or current value changes about a different value and reverses the path from time to time.

Most home and industrial systems and appliances today are powered by alternating line current. All DC-based (direct current) battery-connected devices are recharged operating technically based on alternating line current. All DC devices use DC power derived from AC generators to charge their power system and batteries.

The alternating circuit was formed for the first time in the 1980s when Tesla aimed to solve the failures of Thomas Edison's DC generators.

There are different types of AC circuits:

• AC resistant circuit (R),
• Capacitance AC circuit only (C),
• Inductance AC circuit (L),
• RL Circuit combination,
• AC circuit containing resistant circuit and power (RC),
• AC circuit containing inductance and capacitance (using capacitor) (LC),
• Inductance resistance capacitor (RLC) AC circuit

Various terms commonly used in the AC circuit

• Apparent power is the product of root mean square (rms) values of current and voltage. It is measured in volt-amperes or kilo-volt amperes (kVA).
• Reactive power is the product of apparent power and sine of the angle between voltage and current. This is also called wattless power and is expressed in reactive volt-amperes or kilo-volt amperes reactive (kVA R).
• True power is the product of the apparent power and the power factor. It is expressed in watts or kilo-watts (kW).
• Power factor is the ratio of true power to apparent power. It is a diensionless quantity. It is never be greater than 1 and is expressed either as fraction or as a percentage.
• Q-Factor of Coil is the reciprocal of power factor. It is also known as the figure of merit of a coil or quality factor.

What is the phasor and phasor diagram in a Single-phase AC circuit?

Vectors have both magnitude as well as direction. The sinusoidal variable value can be represented by a rotating line called the Phasor. Phasor is a straight line rotating anticlockwise at a constant angular velocity. The waveform and mathematical representation of alternating quantities are shown in the diagram given below. This is sinusoidal. The majority can be represented using phasors.

Advantages

• Used where small power is required to run any appliance. For example in heaters, coolers, lights, fans, etc.
• Simplified design and operation of the power supply.
• Adequate for carrying loads up to 2.5 kW.

Disadvantages

• Cannot be used where heavy loads are run. For example in industries, factories, etc.
• Requires a supplementary circuit for operation of motors less than 1 kW.

EMF generation in a Single-phase AC circuit

In Single-phase EMF generation an alternating voltage can be generated

• By rotating the coil in the magnetic field
• By rotating the magnetic field inside the immovable coil

The amount of electricity generated depends on

• Number of turns on the coil
• Field strength
• Speed

Use of a Single-phase AC circuit

Single-phase power generates electricity for living rooms and household appliances, as many electrical appliances require less energy to operate. These appliances include fans, heaters, televisions, refrigerators, and lamps.

Context and Applications

In each of the expert exams for undergraduate and graduate publications, this topic is huge and is mainly used for:

• Bachelor of Technology in the electrical and electronics department
• Bachelor of Science in physics
• Master of Science in physics

Common Mistakes

Remember that, positive power equals negative power. So, the power in the center of the circuit is equal to zero.

Related Concepts

• Single-phase DC circuit
• Three-phase AC circuit
• Three-phase DC circuit
• Single-phase transformer
• Three-phase transformer

Practice Problems

 Q1  In case of Inductive circuit, frequency is ___________ proportional to the current.

(a) directly

(b) inversely  

(c) both

(d) no effect

Correct option- (b)

Explanation- The formula for current in inductive circuit is $i=\frac{V}{2\pi fL}$, where V is voltage, f is frequency and L is inductance . Therefore, f is inversely proportional to i.

Q2   In an AC circuit, a low value of KVAR compared with KW indicates _________.

(a) low efficiency

(b) high power factor

(c) both

(d) none of these

Correct option- (b)

Explanation- In an AC circuit, a low value of KVAR compared with KW indicates a high power factor.

Q3  The time it takes for an alternating current to complete a single cycle is called

(a) time rate

(b) time period

(c) waveform

(d) frequency

Correct option- (b)

Explanation- The time it takes for an alternating current to complete a single cycle is called time period. It is inverse of frequency.

Q4 The total instantaneous power supplied by three-phase AC supply to a balanced R-L load is_________.

(a) zero

(b) constant

(c) both

(d) none of these

Correct option- (b)

Explanation- Total instantaneous power supplied by a 3 – φ AC supply to a balanced RL or RC load is always constant.

Q5 The unit for reactive power is _________.

(a) KVA

(b) KVAR

(c) KW

(d) none of these

Correct option- (b)

Explanation- The unit for reactive power is KVAR.