TPT May 2023

ARTICLE

Thermatool Corp

Energy efficiency and high frequency tube and pipe welding By Olexandra Tupalo, manager, Thermatool Labs

In most cases, potential energy is considered, which is the energy stored due to the relative positions of charged particles or electric fields. Electrical power is denoted by P and measured using the unit Watts. In the HF welding context, it is a high frequency current circulating in an induction coil that generates a magnetic field that induces a current in the strip edges that form the weld vee. What is efficiency in HF welding? To understand the power delivered to the load, you need to understand where the losses are. The schematic shows four sources of energy transformation related to power ratings for HF welding power supplies: 1. DC output power – rectifier efficiency is AC input to DC output. 2. Inverter – focus on MOSFETs (Si MOSFETs, SiC MOSFETs). a. IGBTs are not known as efficient switching devices for high frequency (>150kHz) welding applications. b. Si MOSFETs in a properly designed HF circuit are 95% + efficient. c. SiC MOSFETs in a properly designed HF circuit are 96% + efficient. 3. At lead set – HF generator including the output bus. The power supply rating at the lead set flange is used by other power supply manufacturers. 4. Thermatool calorimetric rating and calibration – the rating that matters to customers.

This article will define the fundamental meaning of energy as it relates to high frequency (HF) tube and pipe welding. It is important to distinguish HF welding from arc welding processes, as the energy in these processes will have a slightly different meaning. For example, most readers will be familiar with arc energy (AE), which is a measure of how much energy was applied to the workpiece to form a weld in arc welding processes. To define what energy is used in HF welding, let us first define what energy is in electrical terms. Energy is often defined as the total amount of work done to make current flow through an electrical circuit. The basic unit of electrical energy is the joule or watt-second. Electrical energy is said to be one joule when a current of one ampere flows through a circuit for one second when a potential difference of one volt is applied across it. The commercial unit of electrical energy is the kilowatt-hour (kWh). When we talk about HF welding, it is often noted that power and frequency are the key process parameters. The term “frequency” has a fairly straightforward meaning; however, power can have many definitions depending on the process. Let us first define what power means and how it relates to energy, and only then can we define the power associated with the HF welding process. Electric power is often defined as the rate at which work is done or energy is transformed in an electrical circuit. Simply put, it is a measure of how much energy is used in a given amount of time. Strictly speaking, energy is not generated or used; it is converted from one form into another. In physics, the rate of transfer of electrical energy by an electrical circuit per unit of time is called an electrical power. Here electrical energy can be either kinetic energy or potential energy. 1 Watt is a Joule/sec; 1 W ⋅ s = 1 Joule 1kWh = 1,000 W x 60 sec x 60 min = 36 x 10 5 W ⋅ s or Joules

Figure 1: Input to output power schematic

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MAY 2023