Protecting the system from insulation failure while also maintaining system operation is the primary goal of insulation. The objective is to affordably secure a system without sacrificing reliability.

Various Insulation Approaches

Functional insulation, basic insulation, and protective separation (including supplementary, double, and reinforced insulation) are the three main categories used for identifying insulation types, as shown in Fig 1.

Fig. 1. Insulation types

Functional Insulation

The term "functional insulation" refers to the ability of subsystems, subassemblies, building blocks, or components to withstand internal voltage potential changes as well as the related electric field (E-field) stresses that are generated inside their own environment.

Its main goal is to safeguard the system from events like electric arcs, ignitions, spikes, and fires that may otherwise hinder a device from operating steadily. Certifiable qualifying and production tests are used in this process.

Functional insulation in Power Electronic Converter

If the power electronic converter has a high-frequency isolation transformer, the functional insulation covers the enamel insulation of the copper wires, the inter-winding insulation between the primary and secondary windings, and the insulation between the windings and the core.

In the case of PEC, which is made up of subcircuits that are electrically separated from each other by a high-frequency transformer, a battery of component-level tests is done on the transformer to make sure it works reliably before it is added to the system. The standards used to build the generator are different.

Functional Insulation in Power Electronic Building Block

The packaging of power electronic assemblies into enclosed Power Electronic Building Blocks (PEBBs) with medium voltage ratings of up to 6 kV has received a lot of interest lately. These PEBBs enable the modular system design of PECs with the ability to handle voltages across the entire MV range.

The dense packing of low-power control elements near MV-rated components and bus bars has received a lot of attention. Here, only heat sinks and chassis frames are floating with regard to the overall system chassis ground; an insulation design must take place within the PEBB using the same procedure as insulation coordination at the system level.

When looking at the system as a whole, the internal PEBB insulation system produces functional insulation at the PEBB level. The PEBB's insulation coordination with the rest of the system necessitates protective isolation and added voltage protection for the basic insulation.

Basic Insulation

Insulation that is necessary to offer a basic level of protection against electric shocks is referred to as basic insulation. The safety of people and the functionality of equipment depend heavily on basic insulation to isolate exposed grounded portions from the MV grid-supplied circuits.

Objectives of Basic Insulation

Magnetic cores, ungrounded heat sinks, solder junctions, terminal connections, windings, electrical assembly enclosures, and PEBB enclosures must all be physically separated according to the basic insulation requirements. Additionally, it requires that these energized components be kept apart from the grounded enclosures and equipment chassis.

For all applications, the definition of basic insulation is the same in all insulation coordination standards. It defines the temporary overvoltage levels and basic insulation level impulse voltage that serve as the basis.

One of the main objectives of basic insulation is to ensure that the grounding of exposed parts as a result of a functional insulation failure does not endanger life. Testing is necessary to confirm the effectiveness of liquid or solid insulators to meet the basic insulation requirements.

When it comes to MV systems and MV interfacing PECs made up of building blocks, the basic requirement sets the voltage separation lengths inside the equipment enclosure and at the terminals that connect to the MV grid. Intentionally energized electrical connections and accidental energization of conductive equipment and component surfaces are both covered.

Supplementary Insulation

Supplementary insulation is a distinct extra layer of insulation applied in complement to basic insulation to lower the danger of electric shock in the case of insulation failure.

In the event that the basic insulation fails, this layer of insulation is meant to shield the user from potentially dangerous voltages. When a power supply lacks a safety ground, supplementary insulation is added on top of the basic insulation.

Double Insulation

Double insulation is the process of increasing protective isolation by doubling the thickness of the basic solid insulator. It is primarily thought of as a backup layer of insulation that makes sure the fundamental requirements for insulation are maintained even in the event of a failure in one layer.

Double insulation can fulfill the function of reinforced insulation, which is to guarantee a greater isolation distance for safety reasons, provided that it can be tested and verified.

Although double insulation suggests an extra safety barrier, regulations require testing to confirm that no amount of leakage current in the system will cause touch voltages to rise above acceptable levels.

Reinforced Insulation

Increases in the basic insulation air clearance or insulation thickness of solid or liquid basic insulation are referred to as reinforced insulation. Providing a secure isolation barrier between circuits or circuits that a user can touch is the main function of reinforced insulation.

Double Insulation Vs Reinforced Insulation

The primary distinction between double and reinforced insulation is that in double insulation, another layer of insulation is added to achieve the desired increase in insulation, whereas, in reinforced insulation, increased insulation above the basic requirement is achieved by increasing the distance (through the air or solid insulation) above the basic requirement.

When it comes to design, the best ways to address the need for protective separation are by using reinforced insulation, stand-offs, and maintained separation distances to provide air clearances.

Protective isolation by reinforced insulation is crucial for powering electronic-based systems and PECs from the perspective of equipment dependability and performance. By using this method, the uncertainties related to solid insulator partial discharge (PD) are avoided.

Objectives

Reinforced insulation specifically refers to the connections between low-voltage control hardware, sensors, and protective monitoring circuitry that are located within the same enclosure as and adjacent to MV-energized system components.

Protective separation combines this close proximity with high voltage change rates (dv/dt) linked to switching power conversion to ensure self-immunity against and self-compatibility in the presence of electromagnetic interference (EMI) noise byproducts.

In addition to providing an extra safety margin between the primary and secondary windings, the windings and the core, and the conductors and shields, reinforced insulation is also applicable to transformer-isolated PEC terminals.

It is crucial that the functional insulation of the transformer, which provides internal galvanic isolation, is not compromised at the sites of entrance and departure due to electric field non-uniformities at the three points of interface.

Summarizing the Key Points

● Insulation is crucial for ensuring the reliability of power electronic converters.

● The three main categories of insulation are functional, basic, and protective separation (which includes supplementary insulation, double insulation, and reinforced insulation).

● Functional insulation is a key approach that enables subsystems, subassemblies, building blocks, or components to withstand internal voltage potential changes and electric field stresses.

● Certifiable qualifying and production tests are used to ensure the effectiveness of insulation techniques and maximize system dependability.

● Effective insulation strategies can help protect high-voltage systems from insulation failure while maintaining system operation and reliability.