Name: bil and surge protection for power equipment
Uploaded: 2024-11-21T14:54:42.000Z
Duration: 1 min 23 s
Channel: JoVE

Electrical insulation, as seen in household wiring, is crucial for safety, preventing electric shock and short circuits by covering conductive materials with insulating materials such as plastic or rubber.
The strength of equipment insulation varies with time, but it can withstand high transient overvoltages, provided they are short-lived.
For testing insulation strength, a standard impulse voltage wave is used. This wave shape is defined by the time it takes for the voltage to reach its peak and decay to half its peak value.
The peak value of this defines the Basic Insulation Level, or BIL. Equipment meeting standard BILs can endure repeated applications of the standard waveform without insulation failure.
Some equipment, like overhead transmission line insulation, is self-restoring after a short circuit, whereas internal transformer insulation requires repair or replacement upon failure.
Protective devices, connected in parallel with the equipment from each phase to the ground, safeguard the equipment against overvoltages exceeding its BIL, providing a protection margin.
A simple example of a protective device is the rod gap, designed to spark over at specified overvoltages. &#160;

insulation coordination

Insulation Coordination

Insulation coordination is the process of matching electric equipment&#39;s insulation strength with protective device characteristics to protect the equipment against expected overvoltages. This selection is based on engineering judgment and cost. Equipment can generally withstand short-duration high transient overvoltages, but repeated tests with identical waveforms can yield inconsistent results. As a result, standard impulse voltage waveforms are used for testing, defined by specific times for the voltage to peak and decay to half its peak value.
The Basic Insulation Level (BIL) is defined as the peak value of the standard impulse voltage wave. Standard BILs, as defined by the IEEE, ensure equipment can withstand repeated applications of this waveform without insulation failure. These BILs apply to all equipment, regardless of grounding. In practice, BILs are often expressed in per-unit values.
Protective devices play a crucial role in insulation coordination. They are typically connected in parallel with the equipment and designed to limit voltage to a level below the equipment&#39;s insulation withstand capacity. The protection margin is the difference between the equipment breakdown voltage and the protective device ceiling voltage.
Protective devices must meet several criteria: provide high impedance during normal operation to minimize losses, low impedance during surges to limit voltage, effectively dissipate or store surge energy, and return to open-circuit conditions after the surge.
Common protective devices include rod gaps and surge arresters. Surge arresters can be of various types, including air-gap with resistors or gapless designs, and they operate by limiting voltage and dissipating energy during overvoltages.
Effective insulation coordination ensures the reliable operation of power systems by protecting equipment from overvoltage damage, as a result, maintaining system stability and longevity.

Electrical insulation, as seen in household wiring, is crucial for safety, preventing electric shock and short circuits by covering conductive materials ...

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JoVE Core

Electrical Engineering

Unit 1

Transmission Lines: Transient Operation

KEY TERMS AND CONCEPTS

bil and surge protection for power equipment

Insulation coordination matches electric equipment insulation strength with protective device settings to guard against expected overvoltages. Engineers choose these levels using judgment and cost. The goal is to keep equipment safe while avoiding unnecessary expense.

Equipment can usually survive short, high transient overvoltages. Repeated tests with the same waveform can still give inconsistent results. For that reason, standard impulse voltage waveforms are used in testing. These waveforms are defined by the time it takes the voltage to peak and the time it takes to fall to half its peak value.

The Basic Insulation Level, or BIL, is the peak value of the standard impulse voltage wave. IEEE standard BIL values help show that equipment can withstand repeated applications of this waveform without insulation failure. These BIL values apply to equipment regardless of grounding. In practice, BIL is often written in per-unit form.

Protective devices are a key part of insulation coordination. They are usually connected in parallel with the equipment and are designed to keep voltage below the insulation withstand level. The protection margin is the difference between the equipment breakdown voltage and the protective device ceiling voltage.

A protective device must have high impedance during normal operation so losses stay low. It must also have low impedance during a surge so it can limit voltage. It should absorb or store surge energy, then return to an open-circuit state after the surge ends. Common examples include rod gaps and surge arresters, such as air-gap designs with resistors or gapless designs. Surge arresters limit voltage and dissipate energy during overvoltages, helping power systems stay reliable, stable, and long-lasting.

BIL and Surge Protection for Power Equipment

bil-and-surge-protection-for-power-equipment

traveling waves: lossless lines

Wave Speed on Lossless Transmission Lines

Traveling waves on a lossless transmission line are shaped by the line’s inductance and capacitance. The model starts with a single-phase, two-wire line of length Δx. It has loop inductance L H/m and line-to-line capacitance C F/m. A short section of the line can then be treated as a series inductance LΔx and a shunt capacitance CΔx. Voltage v(x,t) and current i(x,t) are written for any position x and time t along the line. Kirchhoff’s Voltage Law, or KVL, is used for the voltage relation.

boundary conditions: lossless lines

Transmission Line Reflections at Both Ends

Single-phase, two-wire, lossless transmission lines show how voltage and current waves reflect at both ends of a circuit. In this model, the line has a length, a surge impedance, and a wave velocity. These are set by the line’s inductance and capacitance per unit length. A home electrical wiring system can be treated this way in a simple circuit model. At the receiving end, the boundary condition says that the voltage equals the receiving-end impedance times the current. This relationship is...

bewley lattice diagram

Tracing Transient Waves with a Bewley Diagram

The Bewley lattice diagram organizes voltage-wave reflections in transmission-line transients. It helps students follow how a signal moves along a line and bounces back from each end. The diagram was developed by L. V. Bewley. The vertical axis shows transient time, and the horizontal axis shows the line position x. Diagonal lines show traveling waves. These lines make the wave motion easier to read because each segment marks a wave moving through the line. Each reflection is found by...

lossy lines and overvoltages

Signal Attenuation and Power Losses

Transmission lines with series resistance and shunt conductance can weaken signals, change wave shape, and waste power. These effects are called attenuation, distortion, and power losses. They matter in long power lines and other practical transmission systems. When constant resistance and conductance are present, the voltage and current equations change. The propagation constant shows that the wave includes both forward-traveling and backward-traveling parts. As the wave moves along the line,...

Insulation coordination matches electric equipment insulation strength with protective device settings to guard against expected overvoltages. Engineers choose these levels using judgment and cost. The goal is to keep equipment safe while avoiding unnecessary expense. Equipment can usually survive short, high transient overvoltages. Repeated tests with the same waveform can still give inconsistent results. For that reason, standard impulse voltage waveforms are used in testing. These waveforms...

key terms and concepts

Learn how BIL, impulse testing, and surge arresters help match insulation strength with overvoltage protection in power equipment.

BIL and Surge Protection for Power Equipment | JoVE K12

JoVE Core Electrical Engineering offers easy-to-understand animated videos that cover fundamental concepts of electric circuits along with circuit analysis techniques. It incorporates first-order and second-order circuits using operational amplifiers and circuit transformation concepts. The inclusion of practical design examples and real-world applications through scientist-in-action videos adds significant educational value, making complex concepts accessible.

BIL and Surge Protection for Power Equipment

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