Tech Tips

High voltage power supplies must be handled with care.
"We use ours carefully, so we'll be fine."
"We never had any problems, so we're probably ok."
... But, are you sure there is nothing you've neglected or overlooked?

Let Matsusada Precision, which specializes in the manufacture of high voltage power supplies, show you the correct way to use a high voltage power supply.

Safety and Usage of High Voltage Power Supply 1

To prevent discharging

Even for insulators, various discharge phenomena are likely to occur as the applied voltage increases. Therefore, when handling high voltage, it is extremely important to ensure withstand voltage for safety. Withstand voltage is determined by the creepage distance and insulation distance of the insulator, and the shape of the electrode.

  • Creepage distance: This is the distance along the surface of an insulator between two conductive parts.
  • Insulation distance: This is the thickness of the insulator when the conductive parts are completely covered by the insulator.

The withstand voltage decreases due to humidity and dirt/dust, and discharge and leakage are more likely to occur as the voltage increases. Choose an appropriate insulating material for the voltage to be used, so that the insulation can be maintained for a long time.

A variety of insulation methods are described below.

Air insulation

When conductive parts are exposed to the air, it has insulation properties of about 500 V/mm under dry conditions. However, these insulation properties are adversely affected by humidity, dust, salt, and hazardous gas, and therefore countermeasures are required.

  • Up to about 3 kV can be routed through air and over printed circuit boards. However, this is suitable only for environments with low humidity and no dust.
  • At 6 kV or more, coronas are likely to occur if there are sharp points, such as solder on conductive parts.
    Make sure there are no sharp points on conductive parts.
  • At 10 kV or more, coronas are even more likely to occur. We recommend that you use round electrodes and completely cover the conductive parts with the insulator.
  • At 30 kV or more, discharge tends to occur easily, and therefore measures to reduce the electric field, such as a corona ring, are required.
Gas insulation

SF6 gas is commonly used. It has high dielectric strength and is chemically stable up to a gas temperature of 1800 K. It has a withstand voltage of about 8 kV/mm.

Liquid insulation

Petroleum oils, silicon oils, and fluorinated oils are a few examples of insulation oils.

Solid insulation If the voltage to be used is 3 kV or less, most resin materials (with high insulation resistance) can be used. At 10 kV or more, we recommend the use of materials with especially high insulation properties.
  • * Note that bakelite and phenolic materials will result in large leaks.
  • * Epoxy and silicon resins are often used when potting. In some cases only one liquid is used, and in other cases two liquids are mixed together to form the resin. They have a high withstand voltage, and therefore it is possible to shorten the insulation distance.

Safety and Usage of High Voltage Power Supply 2

Handling high voltage output cables

There are a variety of ways to make connections when applying high voltage. Here we describe an example method for handling high voltage cables, and precautions that should be observed.

For direct soldering

In order to avoid discharging electricity in a manner that will cause bodily harm, either cover the object with an insulator that has sufficient dielectric strength, or cover it with an object that has ground potential so that electricity is not discharged to a different location.

Secure the cable in a mechanically method so that any force exerted on the cable may not concentrate on the soldered area.
Secure the cable in a mechanically method so that any force exerted on the cable may not concentrate on the soldered area.
When connecting high voltage cables together

When connecting high voltage cables together to create a long high voltage line, it is difficult to keep them connected simply by linking them together as described above. Therefore, cover the connections with heat-shrink tubing that has dielectric strength. Note that there is a risk of dielectric breakdown in the tube if its withstand voltage is not sufficient.

If the insulation withstand voltage of a single tube is not sufficient, use double or triple tubes to ensure sufficient withstand voltage. In addition, if there are rough surfaces on the solder, dielectric breakdown might occur even if the tube has sufficient insulation withstand voltage. Please be sure to make rounded solder joints.

Cover the connections with heat-shrink tubing that has dielectric strength.

Smooth the soldered area to finish it so that no "pointed" edges can be seen.

Good
The connections making rounded solder joints with tubing
No Good
The connections making in the pointed edge solder

Safety and Usage of High Voltage Power Supply 3

Items that require particular attention

When handling high voltage, failure to observe safety precautions can result in electric shock, or even death in the worst case. Be sure to carefully observe the following safety precautions.

1. Always connect a ground wire

In order to avoid discharging electricity in a manner that will cause bodily harm, either cover the object with an insulator that has sufficient dielectric strength, or cover it with an object that has ground potential so that electricity is not discharged to a different location.

2. Do not touch high voltage areas

When operating equipment, avoid contact with parts that output high voltage as well as high voltage terminals.

Otherwise, electric shock could occur. During normal operation and test operation, extremely high voltage is applied to the terminals. Touching them could lead to a fatal accident.

3. Cover high voltage areas

With high voltages of 300 V or more, there is a risk of electric shock due to the discharge of electricity even if you do not touch an electrode directly. Either cover electrodes and other high voltage areas with insulators that have sufficient dielectric strength, or cover them with grounded conductive material, to ensure that these areas cannot be touched directly.

Safe
Cover with Insulators.

Use insulators having high insulation property

Danger
Cover with Insulators.

Never touch stripped wire

4. Share an awareness of danger

Considering the risk of electric shock accidents, if personnel who are experienced in the operation of high voltage power supplies and who know how to perform appropriate first aid measures are not nearby, avoid any contact with high voltage power supplies. In addition, if inexperienced personnel will be operating a high voltage power supply, explain the necessary precautions in advance (such as avoiding contact with hazardous areas) and make sure they completely understand the dangers before allowing them to perform the operations.

5. Perform operations with your right hand

In order to reduce the risk of electric current flowing through the important organs of your body even in the event of electric shock, be sure to operate high voltage power supplies with only your right hand while keeping your left hand away from the high voltage power supply and all other equipment.

6. Turn off the power before touching equipment

Be sure to turn off the power before touching any high voltage areas. Or, make sure that the power has already been turned off. There are capacitors in the output area, which makes it extremely dangerous to touch that area immediately after the power has been turned off. Pay careful attention to the electric charge in these capacitors while connecting them all to ground to discharge the electricity.

7. Pay attention to electric charge in cables

The energy that is charged in output shielded cables is discharged by grounding. However, when the ground is disconnected, in some cases the charge might not have been completely discharged, or the charge might be recovered after some time has passed. Be sure to completely remove all charge from output cables before touching them.

Short the output to ground.

8. Disconnect the input line before touching

If you have to touch the inside of the power supply for some reason, follow the instruction manual and turn off the power before disconnecting the input line. And, all the capacitors as well as devices that generated high voltage must be connected to the earth.

In case there is no procedure described in the instruction manual, never remove the cover and do not touch the inside of the power supply.

9. Instruct others to pay careful attention

In order to prevent people from entering hazardous areas or inadvertently coming into contact with high voltage areas, clearly mark hazardous areas and instruct others to pay careful attention to the dangers of high voltage. In addition, when high voltage is generated, issue a warning with a warning lamp or an audible alarm.

No trespassion

Danger! HIGH VOLTAGE

NO TRESPASSING

Electric Shock

Electric shock, or electrocution, refers to the flow of electric current through the human body. The degree of electric shock is related to the value of the current that flows through the body, and the path through which the current flows. While weak currents will produce only a tickling feeling, they could also cause burns, respiratory problems, cardiac impairment, or in the worst case the loss of life.

For a voltage of 100 V, the resistance of human skin is approximately 5 kΩ in dry conditions. In wet conditions, it drops to about 2 kΩ. The resistance of the human body is approximately 300 Ω. If you come into contact with 100 V while your skin is wet, about 22 mA of electric current will flow through your body and you will not be able to break off contact on your own.

This is why performing any operations with wet hands is strictly prohibited.

Electric current value Effect on human body
1 mA Mild tingling
5 mA Considerable pain
10 mA Unbearable pain
20 mA Intense muscular contraction, unable to break away from circuit on one's own
50 mA Considerably dangerous
100 mA Fatal consequences

These numerical values are conceptual. If only a weak current flows either because the capacity of the power supply is extremely small or the impedance (similar to resistance) of the circuit is large, the danger will be less. As voltage increases, the air insulation is broken and electricity is discharged, leading to an increased risk of electric shock even if without direct contact with an electrode. Maintain a safe distance from charged areas, as shown in the following table.

Care must be taken to avoid approaching these charged areas.

Voltage of charged area (kV) 3 6 10 20 30 60 100 140 270
Safe distance (cm) 15 15 20 30 45 75 115 160 300

First Aid for Electric Shock

Rescue

Immediately move the victim away from the conductor through which the electric current is flowing. At that time, avoid direct contact with both the conductor through which the electric current is flowing and the body of the victim, to avoid becoming subject to electric shock yourself. Immediately turn off the high voltage power supply and ground the circuit. If the high voltage power supply cannot be turned off, either ground the circuit or use an axe with a dry wooden handle to cut the input and output cables. In that case, take care that electric sparks are not discharged from the cables. If it is not possible to either turn off or ground the circuit, use an insulator such as a dry board or clothing to rescue the victim. Call an ambulance immediately.

Symptoms

Do not confuse the symptoms of electric shock with death. In addition to severe burns, the symptoms of electric shock also include unconsciousness, respiratory arrest, cardiopulmonary arrest, paleness, and rigidity.

Treatment

  1. If the victim is not breathing properly, immediately start artificial respiration on the spot. Note that the victim should be moved to a safe location only if the lives of the victim or rescuers are in danger by remaining at the accident site.
  2. If you start artificial respiration, continue performing artificial respiration correctly either until the victim begins breathing again on their own, or until medical professionals are able to take over.
  3. If there is another person available to perform artificial respiration with you in alternating turns, do so continuously without interrupting the rhythm. Electric shock might also cause burns inside the body, which can lead to serious consequences if left untreated.

Therefore, in addition to first aid, be sure to have the victim examined by a physician as soon as possible.

Although we have described the measures that should be taken in the event an accident occurs, it goes without saying that the best action is to prevent accidents from occurring in the first place. Please develop a thorough understanding of the dangers of high voltage, and use high voltage power supplies both safely and correctly in order to ensure that electric shock accidents never happen.