High voltage (HV) cables are the safe way to use and transfer large quantities of electricity at one time. These cables come in a variety of types which are designed for use with different types of machines and voltages of electricity (Swain, 2012). One of the ranges of application is vehicle's primary ignition wires.
General Information
The main purpose of HV cables is to transfer electric impulses from an ignition coil to sparking plugs. Consequently, HV cables must: (a) withstand high voltage (up to 40000 V); (b) transfer impulses with minimum losses; (c) provide minimum radio interference; (d) have good insulation to prevent current leakage; (e) maintain their properties in wide temperature range (from -30ºC in winter up to 100ºC during vehicle operation in summer).
To transfer high voltage impulse with minimum losses, it is necessary to minimize electrical resistance of wire. That is why a copper lead of a cable was used for a long time before but when different radioelectronic devices (radio sets, TV sets, electronic instrumentation system, etc) started to be used massively, main copper wire disadvantage was discovered – emission of powerful electromagnetic interference.
To reduce electromagnetic fields in high voltage circuit of ignition system, additional electrical resistance is used. It can be built in a distributor rotor (runner), a sparking plug or its cap in different combinations. Besides, a carbon electrode in a distributor cap also has resistance.
Nowadays the most effective and widespread way of reducing radio interference is using high voltage cables with distributed resistance.
HV Cables Structure
Up-to-date HV cables consist of a lead of a cable, insulation, metal contacts, and caps (see Figure 1).
Figure 1. High voltage cable: 1 – safety caps, 2- metallic contact, 3 – insulation, 4 – a lead of a cable.
Lead of a Cable
There are several types of a lead of a cable: (a) a copper multiple-core one with resistance 0.02 Ohm/m (additional interference suppression resistors are needed); (b) nonmetallic with metallic winding one – distributed resistance up to 2 kOhm/m (A central part of a core is made of glass fibre impregnated with graphite, flaxen thread or kevlar. Thin metal wire is wound above. As a rule interference suppression resistors are needed); (c) nonmetallic one with high distributed resistance (No additional resistors are needed. It can be made of cotton yarn impregnated with carbon-black solution, polymeric material or fiberglass threads with graphite dust).
High Voltage Cable Insulation
HV cable insulation is a single-layer or multilayer protective dielectric coating of a lead of a cable. It is designed to prevent current leakage, to protect the wire from moisture, fuels and lubricants, harmful steams, temperature in engine compartment, and mechanical damage.
Insulation is made of different types of plastic, silicone, and rubber in different combinations. Sometimes mechanical strength of insulation is improved due to fabric, cotton, glass-fabric or polymeric braiding.
Metal contacts provide electrical connection between a lead of a cable and relevant contacts of a sparking plug and an ignition coil or a distributor cap.
References
Swain, K. (2012). High Voltage Cable Types. Available from eHow Web site: …