Electrical power surges definition
Electrical power Surge is a voltage spike that is fast, of high rate rise and of a short duration electrical transients. There are many reasons for electrical power surge, they are; Overvoltage, switching of electrical loads, magnetic and inductive coupling, Lightning, power outages, damage or exposed wiring, overloaded circuits, static electricity, motor/power noise and magnetic coupling are among all factors that cause surges. The surge protector provides a simple, economical and reliable protection method for power surge protection of electronic equipment.
It is well known that electronic products in use often encounter unexpected voltage transients , spikes and surges, resulting in damage to the electronic products made of semiconductor devices (including diodes, transistors, thyristors, integrated circuits, etc.) and as a result such electronic products get burned or broken down.
It is estimated that 75% of electronic product failures are caused by transients, spikes and surges. Voltage transients and surges are everywhere, power grids, lightning strikes, blasting, and even people walking on carpets can generate tens of thousands of volts of static-induced voltage, which are invisible killers of electronic products. Therefore, in order to improve the reliability of electronic products and the safety of the human body, it is necessary to take protective measures against voltage transients and surges.
Protection Methods against Electrical Power Surges
Method 1: Ground the whole electric machine and power system. The ground (common end) and the ground of the whole machine and the system should be separated. Each subsystem in the whole electrical machine and power system should have an independent public end. Data should be read and transmitted between the subsystems. Again, control signal should be based on the ground level and therefore ground wire line (face) must be able to allow flow of a large current, such as hundreds of amperes.
Method 2: Use voltage transients and surge protection devices in key parts of the whole electrical machine and power system (such as computer monitors) to bypass voltage transients and surges to the subsystem ground and to the earth through the protection device. The transient voltage and surge amplitude entering the whole machine and system are greatly reduced.
Method 3: Combine several voltage transients and surge protection devices for important and expensive machines and systems to form a multi-level protection circuit.
The surge protector provides a simple, economical and reliable protection method for power surge protection of electrical and electronic equipment. Factors to consider when choosing a surge suppressor/protector include; functional range, speed of operation, and whether the device to protect against surges include moving parts. Through surge protection components, the surge energy is quickly transmitted and suppressed like when lightning strikes and operates overvoltage, earth leads function and therefore electrical equipment is protected from damage.
surge protector working principle
Protection Techniques against Voltage and Power Surges
- Parallel surge protector is connected in parallel to the power supply line
Parallel Surge Protective devices (SPDs) generally contain components the clamp and divert voltage transients’ away from the load. The technologies most commonly used are gas tubes, silicon avalanche diodes (SADs) and metal oxide varistors (MOVs). MOVs are voltage sensitive components that begin to conduct current when a transient voltage conditions exists on the line. Under normal conditions, the varistor in the lightning protection module is in a high impedance state. When the grid is subjected to lightning strikes or switching operations, the surge arrester responds within nanoseconds, and the varistor is in a low-impedance state, quickly limiting the overvoltage to a very low amplitude.
When there is a continuous pulse or continuous over-voltage in the line for a long time, the performance of the varistor is degraded and the heat is heated to a certain extent to trip the hot-release mechanism to prevent fire, thereby protecting the electrical device.
- Series filter type surge protector is connected in series to the power supply line
Active Tracking Filters (ATF) was originally designed to protect sensitive equipment from high-frequency noise. Here, a use of low-pass circuit to eliminate high-frequency noise. Low-pass or L-C filters are the most and used for transient reduction and consists of series inductors, capacitors and resistors. ATFs are load dependent, which means that the series inductors located on each phase and neutral conductor are sized to handle the maximum current draw on the line. These inductors together with the capacitors and resistors form a circuit capable of absorbing a large bandwidth of noise. This surge protector provides safe, clean power to valuable electronic equipment. In addition to huge electrical energy, lightning waves have extremely excessive voltage and current rise rates. A shunt-type surge protector can only suppress the amplitude of a lightning wave, but it cannot change its sharply rising leading edge. The series filter type power surge protector is connected in series to the power supply line. Surge components (MOVs) are mounted directly across the lines with no additional lead length
In the case of overvoltage, MOVs (MOV1 and MOV2) respond within the subtle time and clamp the overvoltage. At the same time, the LC filter reduces the steep voltage of the lightning wave, the current boost rate by nearly 1000 times, and the residual voltage by 5 times. Protect sensitive user devices.
- Installing varistor-type components between the phases of the power liness to limit the surge overvoltage
The first method has better protection effect on electrical equipment with high impact voltage level such as lighting, elevator, air conditioner and motor. However, for modern electronic devices with high integration and compact structure, the actual protection effect is not satisfactory. The reasons are as follows:
Taking the inductive lightning protection of a single-phase 220V AC power supply as an example, a common method is to apply a suitable pressure-sensitive component between the zero and ground lines to absorb the spike voltage generated by the induced lightning strike. The lightning protection effect of the power line depends entirely on the selection of the parameters of the pressure sensitive device and the reliability of the operation of the pressure sensitive device.
The varistor limit value is based on 310V peak voltage of the mains plus 20% of the grid fluctuations, 10% of the device dispersion error and 15% of the long-term work caused by heat, moisture, component aging and other reliability. Factor compensation, generally takes values from 470V to 510V. Various spike interference voltages such as inductive lightning strikes are limited to 470V. For voltages below 470V, the varistor does not operate.
The power frequency withstand voltage of ordinary low-voltage electrical equipment (machine tools, elevators, lighting, air conditioners, etc.) is generally 1500V AC, and the instantaneous peak voltage can reach more than 2500V, so the voltage of 470V is very safe. However, the operating voltage of modern electronic devices composed of large-scale integrated circuits is generally between ±5V and ±15V, and the maximum withstand voltage is generally not more than 50V, so the high-frequency spike voltage of less than 470V superimposed on the commercial power will be sent directly into the load, through the space coupling capacitor, transformer inter-layer, inter-electrode capacitance is disproportionately transmitted to the switching power supply or integrated circuit chip, which can cause malfunction.
Although high-frequency switching power supplies and electronic devices have corresponding anti-spike interference measures, the cost and volume are limited, and the intensity and spectrum of spike interference such as inductive lightning strikes vary greatly, so the protection effect is not satisfactory. This is also the result of the ideal varistor limiting element. In fact, due to the residual voltage of the varistor and the inductance of the lead and under the strong inductive lightning strike, the actual limiting voltage peak may rise to 800V and at 1000V or more, and the subsequent electronic equipment is threatened.
- Surge Isolation Method
Strengthen the protection effect on electronic equipment, and insert a super-isolation transformer (also called isolation method) between the power supply and the load to isolate high-frequency spike interference, and at the same time make secondary equipotential bonding easy.
The isolation method mainly uses an isolation transformer with a shielding layer. Since common mode interference has relatively large ground interference, it is mainly transmitted through the coupling capacitance between the transformer windings. If the shield is inserted between the primary and secondary and it is grounded well, the interference voltage can be shunted through the shield to reduce the interference voltage at the output.
In theory, a transformer with a shield can achieve an attenuation of about 60 dB. However, the quality of the isolation often depends on the process of the shielding. It is best to use a 0.2 mm thick copper plate with a shield on the primary and secondary sides. Usually, the primary shielding layer is connected to the shielding layer of the secondary side through a capacitor and then to the ground of the secondary side. It is also possible to connect the primary side of the shield to the ground of the primary side, and the secondary side of the shield to the ground of the secondary side. And the cross-sectional area of the grounding lead is also larger.
Though this method is a good method for use, it is of a large size and weight or volume. However, this method is too simple for the function of the transformer, and is not easy to install. It has a poor effect on the protection of medium and low frequency spikes and surges, so the market is limited and there are no many manufacturers. Therefore, there are no non-special occasions which are generally used.
- Surge Suppression Method
The absorption or suppression method mainly uses an absorbing device to absorb the surge peak interference voltage. The absorbing devices have the common feature that they exhibit high impedance below the threshold voltage, and once the threshold voltage is exceeded, the impedance drops sharply, thus suppressing the spike voltage.
Such surge or spike suppression devices mainly include varistor, gas discharge tube, TVS tube, solid discharge tube and the like. Different absorbing devices have their own limitations on the suppression of spike voltage. If the current absorbing capability of the varistor is not large enough, the response speed of the gas amplifying tube is slow.
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