FAQs

Dependent on the transformer model, but all flow requirements are listed on the drawings.

We reference RWMA Bulletin 14 in our Universal Manual.

We currently have products in operation for over 20 years in the field. 

Yes, we offer an ERT, which consists of AC water-cooled transformers in combination with SCR Power Controllers, Breaker and CTs inside a cabinet. It allows you to remove the old VRT and place the smaller ERT cabinet in its place.

MFDC stands for Mid Frequency Direct Current, a type of inverter heating technology that uses a mid-frequency AC input (1000 Hz) and converts it to a direct current (DC) output for heating.  The MFDC power supply includes a water-cooled transformer and rectifier potted in a case.

An IGBT (Insulated Gate Bipolar Transistor) functions as a high-speed electronic switch, converting DC power into AC power for controlling power flow in a system.  It is the major component of an inverter which also includes an SCR bridge that converts 3-phase AC to power a DC bus. This technology has been used for automotive resistance welding since the early 1990’s. RoMan Manufacturing currently produces 3000-5000 MFDC power supplies a year to function with IGBT controls.

Frequency and flux density are inversely related in applications like transformers, where increasing the operating frequency allows less core to be used while maintaining the required flux density.  Additionally, MFDC systems are single-phase requiring one core where 3-phase transformers have 3 cores. 

Direct Current provides more stable and steady power flow, reducing thermal cycling, stress, and oxidation on the heating element.  This results in more efficient heat transfer and a longer operating life for the element.

Given the significant reduction in weight of the MFDC power supply, less structural steel is required to support the equipment.  This also allows the MFDC power supplies to be located much closer to the terminal box, reducing the length of the secondary conductors.  Additionally, since the MFDC system is single-phase, one bus from the 3-phase system is no longer required.

Electrical energy is reduced in several ways:

1. The line reactor filters harmonic content from the 3-phase AC line supplying the inverter.  This reduces the gauge of the cable feeding the system.
2. The SCR bridge in the inverter converts the incoming AC power to DC, increasing the power factor.
3. The water-cooled MFDC power supply has less inductive losses than the AC counterpart.
4. The close-coupled MFDC power supply reduces losses in the secondary conductors.
5. The IGBT Control Converts 3 phase AC to 1 phase AC and in the process increases primary voltage to the MFDC power supply. By increasing primary voltage, the transformer can utilize more primary turns. The more primary turns, the less primary current it utilized to reach a given secondary current.   Additionally, the 3 phase input is balanced benefitting the plant’s loading.

MFDC technology has been used in Resistance Welding for nearly 50 years.  It is also used in commercial heat treating, sintering, melting, and electrogalvanizing. 

The highest current at rated voltage that a device is identified to interrupt under standard test conditions. [NFPA 70]

Interrupt rating applies to devices that are intended to interrupt currents, i.e. fuses, circuit breakers.

The prospective symmetrical fault current at a nominal voltage to which equipment is able to be connected without sustaining damage exceeding defined acceptance criteria. [NFPA 70]

SCCR is applied to equipment specific equipment, e.g. industrial control panels, industrial machinery, surge protective devices (SPDs), etc., where the equipment is intended to withstand the applied fault current without causing damage that could create a safety hazard

The National Electric Code (NFPA 70) requires that all electrical equipment that has a SCCR be installed in a location where the SCCR of the equipment is equal to or greater than the calculated fault or short circuit current of the point of application.

An assembly of two or more components consisting of one of the following:

1. Power circuit components only, such as motor controllers, overload relays, fused disconnect switches, and circuit breakers;
2. Control circuit components only, such as push buttons, pilot lights, selector switches, timers, switches, and control relays.
3. A combination of power and control circuit components. These components, with associated wiring and terminals, are mounted on, or contained within, an enclosure or mounted on a subpanel. [NFPA 70]

Industrial control panels are typically used to provide power and controls to industrial machinery and processes. For glass furnaces, the industrial control panel provides overcurrent protection, power control, monitoring, and in some cases, the step-down or step-up transformers used to melt or refine the glass composition at various sections of the process.