Purpose: Withstand testing can be performed on either new or aged cables. The test should only be done if there is concern that cable damage has occurred possibly during installation or the insulation has been compromised due to heat, water or chemicals. General Testing Information • The test can be conducted with AC or DC voltages. • AC Withstand Test for field acceptance is 80% of factory test voltage. See table below. • DC Withstand Test for field acceptance is three times greater than the AC Withstand Test. See table below.
The objective of this procedure is to provide a means of repairing gouges, tears or indents on cables that occasionally happen in the field. Thisprocedurecoversbothmediumvoltageandlowvoltage power cables and will restore the cable back to its original integrity. The purpose of the outer jacket on medium voltage cables and low voltage multi-conducor cables is to protect the underlying components from physical and environmental damage and serves no dielectric purpose. On low voltage single conductor cables, generally, the outer layer is the cables primary insulating layer. For medium voltage cables with damage beyond the outer jacket such as the copper tape shield is torn or on low voltage cables where the conductor is damaged, contact your Southwire Represen- tative. Cable jacket repairs should only be performed by qualified personnel.
Purpose: Insulation resistance testing is a non-destructive test procedure. The test measures the insulation resistance between the phases and/or between phase and ground. It is commonly used in the industry for acceptance testing prior to energizing the cable and for maintenance testing programs. General Testing Information • For single conductor non-shielded cable on a reel, insulation resistance testing cannot be performed due to the fact that low voltage single conductors do not have a grounding conductor, shield or ground plane. • For other cable on a reel, insulation resistance testing can be performed provided the sealing caps are removed. The procedure to test these cables is outlined below. • NOTE: It is important to remove sealing caps from both ends of the cable to be tested. Residue inside the sealing cap can be conductive and lead to false readings.
Did you know that if you run cables that connect your variable frequency drives (VFDs) to your motors you could have a significant safety risk in your plant or factory? Fear not, there is a simple solution to this potential problem. It’s a fact. Non-shielded cables emit noise. In many cases, this is not a significant prob- lem. Most of us have heard that 60 Hz hum that happens when a phone line is run too close to a standard 600 Volt power cable. It’s really nothing more than a nuisance with standard power. But the same physics behind that hum may be creating a safety issue in your facility. VFDs change standard 60 Hz power in to variable frequency power that allow us to ex- perience significant energy savings, better control of our equipment, and reduced main- tenance costs. However, like most things in life, there are trade-offs. The down-side of a drive system is that it generates lots of high frequency voltage components that can cause problems with motors, drives, and other plant equipment. These same high frequency waveform components can also cause safety issues. Let’s look at how.
Insulation compound chemistry has come a long way in todays market. The chemistry for cross-linked polyethylene (XLPE) and ethylene propylene rubber (EPR) changed in the 1960s so modern XLPE and EPR insulations use catalysts that chemically cross-link the molecular chains yet do not corrode the conductor. Similarly, advances in semi-conducting shield compounds deliver far better stripability with bare copper conductors. Corrosion is another reason tinning is considered. Today, there are special electrical contact lubricants such as NO-OX that prevents the formations of oxide films at termination points making tinning less desirable. In conclusion, unless the power cable installation is in an environment that is continuously exposed to corrosive elements (as is the case in certain wastewater treatment facilities), copper conductor tinning is a practice that is no longer required with today’s cable compounds, corrosion lubricants and manufacturing technology. It’s an added cost that also requires longer lead times and minimum run quantities. And since it is an environmentally unfriendly process, any reduction in conductor tinning helps to make our environment better.
Correctly sizing a VFD Cable for your drive and motor is really not difficult if you know where to look. By knowing what sections of the National Electrical Code (NEC) to ref- erence, you can correctly size cable conductor size for your system. Just follow these five simple steps to size cables for low voltage drive systems with operating voltages not greater than 575 volts. STEP ONE: Determine the minimum temperature rating of your equipment. Temperature ratings are important to know when derating the cable for the application as higher temperature ratings allow cables to handle more current. The NEC tables for ca- ble ampacity for low voltage cables have columns for 60°C, 75°C and 90°C. The column you use will be based on the minimum temperature rating of your drive terminals, your motor terminals, and your VFD Cable. Most drive terminals are rated for 75°C. All Southwire VFD Cables carry a 90°C conduc- tor temperature rating but this is not true of all VFD Cables from other manufactures. Motor terminal temperature ratings can vary from 60°C to 90°C. Each of these temperature ratings needs to be verified with the manufacturer’s datasheets or user manuals. If other equipment is being used that is in the cable’s path, like a quick disconnect, collect that devices temperature raring too. Once you have all the temperature ratings, record the minimum value.
Southwire® Industrial Power Cable products do not have a defined shelf life. These products are composed of hard goods (metal, polymer, etc., ...) that are designed for many years of service once installed. As long as the products are not damaged during storage/handling and they are stored in a facility that protects against exposure to weather (sunlight and precipitation), there should be no degradation to the electrical and mechanical performance of the products and no reduction in service life. When storing cable the following precautions should be considered
DC Hi-Pot Testing is used for proof testing shielded cables (5kV to 46kV) in the field. The test can be done at various times such as acceptance of new cable installation, maintenance testing to track insulation degradation and as a pre and post test for splicing existing cables to new ones. The test will expose gross imperfections that are caused by improper handling, installation techniques or termination workmanship. A DC Hi-Pot test is not capable of locating the point of failure, rather it gives you an assessment of the whole system.
Strand-fll sometimes called moisture-block is a tar like substance that is applied between each lay-er of a concentric stranded copper or aluminum phase conductor. During the stranding process and at slightly elevated temperatures this tar like substance becomes fuid enough to be forced through a pump and applied geometrically in such a manner that the interstitial space between every strand is flled with the tar. The tar is then allowed to cool whereas it becomes stable and remains in place.
A dual rated cable is a cable that lists two different voltage ratings on its jacket. For instance, a cable with 115 mils insulation thickness may have a jacket with a print legend that lists both 5kV and 8kV voltages at 133% and 100% insulation levels respectively on it. Therefore, this cable may be used on both 5kV and 8kV systems.