August 2022 Volume 4

MAINTENANCE

comprising the model of the forges’ energy consumption, material heating efficiencies can vary by greater than 50 percent, pound for pound. Presently, the highest claimed efficiency of an induction heating installation is approximately 85 percent. This means that if 1000 kW are put in, 850 kW are retained in the material immediately before forging. The remainder is lost to component heating and the environment. Actual efficiency numbers depend on the practices of the company. Heating efficiencies are often much lower than 85 percent, and it is realistic to experience efficiencies of only 35-40 percent. These abysmal numbers are the outcome of: • Poor production planning (rejecting heated billets and not utilizing ‘holding’ features) • Improperly sized induction coil for material dimensions/ composition • Unsuitable induction frequency or load tuning To put this in perspective, at 40 percent efficiency, if an induction heater uses 2,400,000 kWh annually, the company is paying to send 1,440,000 kWh out the door in the form of heat loss. Improving Efficiency -- Given these examples of efficiency, it is also possible for a company to improve production losses just as much through examining its practices and applying efficiency improving operating procedures. Example of this are: • Ensure coils are properly sized formaterial heating. Oversized coils create unnecessary electrical component heating and waste energy. • Optimize preheat and utilize billet holding features if available. • Consult with the OEM on optimization of ‘Zone’ or ‘Stage’ heating if available. • Ensure frequency is appropriate and induction resonant tuning is optimized. Utility Billing Stemming Profit-Loss to the Utilities -- The ‘utility’ faces costs in gathering, storing, producing, and delivering energy to its customers. Powerplants do not build themselves, transmission lines do not erect themselves, and everything requires periodic maintenance or replacement. All this costs the utility money, and over the years they have become quite creative in exacting this money from their customers. The Forge is Not My Home -- In our residential electric bills we see multiple line items detailing what our costs are. These typically cover generation, transmission and cost recovery.The costs are either a product of electrical consumption (i.e. derived from how many kWhs were consumed in a month), or fixed ratio amounts related to some aspect of electrical delivery. Absent from most of our bills are how we used the electricity, when we used the electricity, and what appliance was powered by the electricity.

All technical differences aside (three-phase versus single-phase, for example), the electrical utility billing structure for a forge has several of the same line items billed to residential customers. It also has unique charges related to the how, when and what the electrical power was used for. Let us investigate this further. Characteristics of a forge as viewed by the electrical utility include: • Creation of high demand loads during press motor start-up • Press motors creation of poor power-factor conditions • Induction heaters creating large harmonic currents • Induction heaters having high overall demand Electrical transmission and distribution networks have a finite capacity and the forge pushes this capacity to the limit. Since the utility does not usually install new substations on the whim of its customers, the billing structure is designed to encourage its industrial customers to use power responsibly and prevent overburdening of the existing infrastructure. To look at how this is accomplished we will consider two significant utility bill line-items unique to industrial consumers, and several strategies to reduce them. Power-Factor and Peak Demand Billing: It’s Strategic but Not Magic --The first, power-factor (PF), is a property of electrical usage that the utility must account for, as it affects the size of the power distribution network (substations and power lines). The type and design of machinery in operation determines the PF. Power-factor is measured in kVAR’s (an acronym for kiloVolt-Ampere Reactive), which is a unit of demand. In billing terminology it is also referred to as lagging reactive demand. In utility billing, PF is measured and billed in the same way as kWdemand. The second, peak demand, is a method of recording the greatest amount of electrical power that a facility used during a specific time-period, then billing the customer at that rate for a longer, pre specified period. For example, if a machine demands 1000 kW for a single 15-minute period, then only 3 kW for the remainder of the month, the utility may have an agreement with the customer to bill the customer for the entire month at the 1000 kWh rate, even though the customer only used it at that rate for 15 minutes. Large motors, as the type used for press flywheels and large hydraulic pumps have starting demand on the orders of 10X to 20X larger than normal operating demands. Peak demand charges are also determined by the time of day and peak rates are often higher in the afternoons and lower at midnight[3]. The reason for this apparently unreasonable billing structure is to encourage responsible power usage and to avoid overloading the power distribution system.

FIA MAGAZINE | AUGUST 2022 14