List-Post: [email protected] Date: Thu, 31 Jul 1997 21:46:12 -0700 From: [email protected] (Jerry Martin)
Jerry, >I've been asked to test a network powered (-130 Vdc) product >to GR-1089-CORE for lightning and power cross. >The problem is that if you apply 1000 V, 10/1000 uSec, 100 A >to tip/ring while the product is powered, you will damage the >power source. >I've looked into using series inductance followed by an MOV >and capacitor, but I'm not sure if all the energy is getting >to the UUT. It's a bit hard to describe a circuit diagram with words, but I'll give it a try. We use a large resistor in series with each of the DC power feed leads coming from the power supply. The value of these resistors is based on how little current the EUT needs to operate. For example, if the EUT can function over an 18,000 kft. loop of 26 gauge wire, maybe 1000 ohms per resistor will still provide sufficient DC current. As an added bit of protection, we place a "primary protector," i.e., gas tube, across the DC power feed leads between the power supply and the series resistors. The relatively large series resistance in the power feed leads means that nearly all of the surge is delivered to the EUT. The gas tube protector should not interfere significantly with the surge and/or power cross being delivered to the EUT, because of the large series resistance to drop the voltage/current. (In fact, it is probably not needed the majority of the time.) Also, the EUT is probably designed with an MOV in its "front end," perhaps not more than 140 or 160 volts. We feed the surge and/or power cross voltage to the EUT via large capacitors (chosen appropriately for voltage and size according to the voltage in question. It is possible to use a neon gas tube for the feed instead of the capacitors, BUT, you will need to adjust your surge voltage up to compensate for the voltage drop across the neon gas tubes! >Another problem is that my tester applies a short to tip and >ring prior to the application of the test voltage. For our Bellcore testing, we use automated power cross and lightning surge equipment that we built ourselves, so we don't have this problem. Also, our "reference ground" for our surge and power cross equipment is NOT connected to earth, which simplifies things. ________________________________________________________________ John Combs, Senior Project Engineer, ITS/TestMark Laboratories Email: [email protected] URL: http://www.testmark.com
