Many facilities require reliable power-control systems to keep HVAC, lighting, and critical equipment running at all times. Replacing outdated control systems is not always the most effective approach.
Douglas H. Sandberg
Prime, emergency, and standby on-site power systems that are more than 10 years old may be outdated and even incapable of providing adequate power to automated systems and conventional power loads that must operate around the clock. Why is that, considering that engine-generator sets and power-transfer switching mechanisms are so durable? There are a number of reasons.
Foremost is that equipment controls become obsolete comparatively quickly. While engine-generator technology has remained fairly consistent, controls have evolved from bulky electromechanical relays to basic transistors and now to programmable logic controllers (PLCs).
Today’s controllers offer tremendous flexibility for designers, owners, and those who maintain them. The control logic remains pretty much the same as with relays, but changes and updates are made within a software program. There’s no need to add relays, timers, or to re-wire components. PLCs are faster, offer greater functionality, and are more precise and reliable than previous control technologies.
Exponential advances in control technology are the primary reason controls become obsolete relatively quickly. The result is an on-site power system that uses a mix of durable machinery (engine-generators, fuel systems, ventilation systems, and load banks) and controls that are subject to premature obsolescence.
This situation creates real problems for building managers, hospital engineers, consultants, and anyone else charged with maintaining life-sustaining infrastructures. It’s a dichotomy and raises a serious question: What can you do?
The first step is to understand the three basic control groups of an on-site power system:
- Sensory inputs. These are sensors that monitor oil pressure, coolant and exhaust temperature, and fuel supply.
- The brain. This is a central controller, such as a PLC, that acts on sensory inputs.
- Active and passive outputs. An active output shuts down an engine when oil pressure drops below a pre-set limit. A passive output turns on an indicator light or sends an alert.
Besides engine-generators, two other systems are required for on-site, power-transfer switches and monitoring and control capabilities.
Automatic transfer switches
Automatic transfer switches also have experienced some of the same issues as engine generators. The switching mechanism has remained durable over many years, while advances in technology have greatly improved control technology. The transfer switch is the system that makes it possible to transfer loads from one power source to another. Without it, on-site power systems as we know them today would not exist.
There are four types of workhorse transfer switches: open transition, closed transition, delayed transition, and soft load.
The open-transition transfer switch breaks from one power source before it connects with another.
The closed-transition transfer switch also breaks from the utility, or normal, source when power fails before connecting to on-site power. When utility power returns, however, this transfer switch transfers loads back to utility power before it breaks the connection with on-site power. This ensures continuous power to critical loads.
The delayed-transition transfer switch delays load transfers to allow large electrical fields, associated with large inductive loads, to collapse before connecting with another power source. This limits potentially damaging in-rush current.
The soft-load transfer switch enables both normal and on-site active power sources to be simultaneously connected to loads. By paralleling the normal, or utility, source and the on-site power source, loads can be “walked” from one source to the other by increasing or decreasing engine-generator loading.
These transfer switches also are available with bypass isolation capability. A manual transfer switch is integrated with the automatic transfer switch, which allows the automatic transfer switch to be taken off line for maintenance while still protecting critical loads.
Monitoring and control capabilities
Advances in technology and computers, and the advent of the Internet, make it possible to be thousands of miles away, yet still monitor the operation of your critical system and, in some cases, control it as well. Controls may be managed with a PC, laptop, or PDA-type device.
Today, real-time monitoring, trending, and management of critical systems are realities from just about anywhere in the world. The ease of operation, flexibility, and functionality offered by current monitoring and control … View More