RLC Circuit:

An RLC circuit (the letters R, L and C can be in other orders) known as  resonant circuit, tuned circuit, or LCR circuit,  is an electrical circuit consisting of a resistor, an inductor, and a capacitor, connected in series or in parallel. The RLC part of the name is due to those letters being the usual electrical symbols for resistance, inductance and capacitance respectively. The RLC circuit exhibits the property of resonance in same way as LC circuit exhibits, but in this circuit the oscillation dies out quickly as compared to LC circuit due to the presence of resistor in the circuit.

 Applications:

Variable tuned circuits

 Filters

 Oscillators

 Voltage multiplier

 Pulse discharge circuit

Single Phase:

In electrical engineering, single-phase electric power is the distribution of alternating current electric power using a system in which all the voltages of the supply vary in unison. Single-phase distribution is used when loads are mostly lighting and heating, with few large electric motors. A single-phase supply connected to an alternating current electric motor does not produce a revolving magnetic field; single-phase motors need additional circuits for starting, and such motors are uncommon above 10 kW in rating.

Standard frequencies of single-phase power systems are either 50 or 60 Hz. Special single-phase traction power networks may operate at 16.67 Hz or other frequencies to power electric railways.

Poly Phase:

A polyphase system is a means of distributing alternating-current electrical power. Polyphase systems have three or more energized electrical conductors carrying alternating currents with a definite time offset between the voltage waves in each conductor. Polyphase systems are particularly useful for transmitting power to electric motors. The most common example is the three-phase power system used for industrial applications and for power transmission. A major advantage of three phase power transmission (using three conductors, as opposed to a single phase power transmission, which uses two conductors), is that, since the remaining conductors act as the return path for any single conductor, the power transmitted by a balanced three phase system is three times that of a single phase transmission but only one extra conductor is used. Thus, a 50% / 1.5x increase in the transmission costs achieves a 200% / 3.0x increase in the power transmitted.

How 3-Phase Works

A 3-phase circuit combines three alternating currents of the same frequency, each 120 degrees out of phase with each other. This produces three separate "waves" of power, as represented below. The power in a 3-phase power supply never drops to zero, but in single-phase the power falls to zero 3 times per cycle. Thus, in a 3-phase power supply, the power delivered is constant.

Single vs 3-Phase power diagram

While actual efficiency depends on the load-to-capacity ratio, the nominal ratio between the efficiencies is 1.5 in favor of 3-phase when comparing single- and 3-phase power.