As noted in an earlier blog post, the tests you run to ensure that airborne utilization equipment is compatible with an aircraft's power system are specified in a series of MIL-HDBKs, specifically MIL-HDBK-704-1 through MIL-HDBK-704-8. To run these tests, a sophisticated power source is essential to simulate various power conditions. In addition, you also need whatever equipment is required to monitor the unit under test (UUT) while running the test.
As the number of photovoltaic power-generation systems continue to increase, the requirements for photovoltaic inverters are evolving as well. Conventional electrical characteristics such as over-voltage, over-frequency, anti- islanding intended to verify the inverter’s ability to tolerate power grid fluctuation are changing to meet varying requirements of the modern grid. In addition, the introduction of new requirements for low voltage ride through, high voltage crossing, and reactive power injection mean the inverter must be able to provide appropriate compensation when these grid conditions occur.
To ensure that aircraft electronics and other electrically-powered equipment will operate reliably once in the air, you must test them under extreme power conditions. In the military world, MIL-STD-704 (now up to rev. F), “Aircraft Electric Power Characteristics,” establishes the requirements and characteristics of aircraft electric power. This standard is not only used by the U.S. military and military contractors, but has also been adopted, either directly or indirectly, worldwide. For example, the Chinese standard, GJB 181, Characteristics of aircraft electrical power supplies and requirements for utilization equipment, is largely based on MIL-STD-704.
One of the problems we frequently encounter in the field is that power supply users fail to take into account the voltage drop in the wires connecting a power supply to a device under test (DUT) or other electronic system. When a load draws a high current, the voltage drop across the power leads could be high enough to cause a device under test to fail or cause a system to malfunction.
Two terms that often get bandied about when describing automated test systems are resolution and accuracy. To get the best results from your power supplies, it is important to understand the difference between these two specifications and how they affect your system.
While these days, computer control is usually the preferred method of controlling a power supply, many AMETEK Programmable Power products, such as the Sorensen SGA Series still offer analog control. Analog control is still used in many industrial applications, and it's also a good choice if you have fairly simple control needs.
Many of AMETEK Programmable Power's AC power sources are designed to work as both standalone units and in multi-box configurations. The California Instruments iX Series AC/DC power sources, for example, includes independent 5 kVA power modules that can be combined into a number of configurations. You might use a single unit as a high-power, single-phase system or configure three units to form a medium-power, three-phase system. This modularity allows you to build a power system that meets your specific needs.
In Part I, we introduced you to the concept of testing equipment for immunity to voltage dips and short power interruptions in accordance with IEC 61000-4-111. In addition to specifying the test waveforms, the standard also specifies AC source requirements for full compliance testing.
Mains voltage dips and short interruptions can be caused by a wide variety of phenomena and can cause equipment to operate unreliability, and in some cases, can damage the equipment. Faulty loads on an adjacent branch circuit, for example, can cause a circuit breaker to trip, and high-power loads such as welders, motors and electric heaters can cause voltage variations. Natural events, such as power lines downed by storms or lightning strikes, may also disrupt mains power.