Association Report: Automatic Residential Controls and the Challenges for Smart Grid

Smart Grid technologies open up possibilities for domestic appliances to optimize energy consumption through interactions with utilities while maintaining grid stability. The challenge for manufacturers and standards developers is to decide on a common communication scheme and to develop appropriate requirements to maintain required safety levels while integrating additional Smart Grid control function into the overall control system. One needs to ensure that communication data will not compromise safety functions under any mode of operation.

Utilities want to distribute power efficiently. For household appliances, this means integrating demand reduction functions. For example, a utility could temporarily shut down an appliance that the homeowner has pre-arranged in exchange for a reduced energy bill. The challenge for manufacturers of automatic controls and appliances is to prevent any reduction in safety while permitting additional control function.

IEC TC 72 has a long history in developing safety requirements for control devices. The need for these requirements is explained by its chairman Japp Dammer, who said, “A very important animal is IEC 60730-2-5, which concerns burner-control systems. Such a system is the heart of a gas- or oil-fired heating appliance.”

Malfunction can lead to fire or explosion, making it the most potentially dangerous application in a home. Burner-control systems were among the first household applications equipped with safety-related software. Electronic controls are now used in many different applications, such as laundry equipment, HVAC, lighting, and energy management.

Because of the possibility of electromagnetic disturbances in the burner-control industry, it was necessary to introduce electromagnetic compatibility and immunity levels. Test levels had to be higher than in normal household appliances to account for the severity of the potential hazard. It was also necessary to specify possible failures or malfunctions of circuit components through risk or fault analyses.

According to Rich Simons of Honeywell, at some point in a product’s life it will fail. “We are primarily concerned with the results of a failure. Controls must be classified as to the severity of the result of a failure.”

For this reason TC 72 has classified controls based on the hazard a failure will create:
  • Class A: Not relied upon for safety, e.g., thermostat, lighting controls.
  • Class B: Intended to prevent unsafe operation, e.g., thermal cut-outs and laundry door locks.
  • Class C: Designed to prevent unsafe hazard, e.g., automatic burner controls and thermal cut-outs.
Classes B and C are designed so that first- and second-fault conditions will result in the device moving into a safe mode under all conditions. Advances in microprocessor technology have led to its widespread use in electronic controls. Micro-electronics and software that perform safety functions must be evaluated so that they meet the same functional safety criteria as other components of the control system.

IEC 61508 Functional safety of electrical/electronic/programmable safety-related systems provides a framework for evaluating risks so that systems can be designed to prevent or control dangerous failures. Devices must be evaluated at various levels-first as a single unit, then as part of a control system, and finally as part of the final application, device, or appliance.

Remote control is a growing concern. Consumers are increasingly looking to interact with their home’s systems and appliances. But what if, before you leave the office, you remotely switch on your oven to 450 DegF so you can throw in a pizza when you get home, only to find your daughter had put her science project samples in to dry at 150 DegF? The intelligent home system must also be part of the same functional safety framework we apply to the control functions and the appliances themselves.

Functional safety, intelligent controls, and the evaluation of software are areas that will have to respond to new technologies and applications. Smart Grid presents challenges to integrate what were previously stand-alone devices into a coordinated system; a system in which appliances talk to each other, adjusting and coordinating their operation and power consumption. All this must be done while ensuring that there is no reduction in the level of safety provided.

Reprinted from electroindustry magazine by permission of the National Electrical Manufacturers Association.   

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