3-Phase Power: Delta vs Wye Explained

Electricity is used to power a multitude of devices that are designed for the convenience and necessity of people and processes around the world. Three-phase power plays a key role in the design of electrical systems, and 3-phase EMI filters are an important part of electrical devices in different markets, primarily in heavy-duty industrial applications. Most devices in industrial applications demand high power to supply enough electricity to support large motors, heating systems, inverters, rectifiers, power supplier and induction circuits. Due to this, high-powered equipment is usually designed for three-phase or poly-phase phase AC power in which the total power demand is divided between many phases optimizing the power system (generation and distribution) and equipment design.

In a 3-phase system, there are three conductors that carry alternating current. These are called phases and are usually referred to as A, B and C. Each phase is set at the same frequency and voltage amplitude but phase shifted by 120° allowing for constant power transfer during electrical cycles.

Three-phase electric power configurations are specifically important because they can support three times the amount of power with only 1 ½ - 2 times as many wires as a single-phase power configuration. This can help reduce the cost and amount of materials required for designing a power system. It can also simplify the motor design by eliminating the need for starting capacitors.

However, converting big power (inverting, rectifying) generates excessive-high frequencies noise (EMI) which is usually the higher-order harmonics of various switching frequencies.

For this reason, 3-Phase EMI Filters become particularly important in 3-phase applications because they reduce the amount of electromagnetic interference, prevent disturbances to the equipment’s operation and help companies comply with EMC regulations.

What Are the Differences Between Delta and WYE Systems?

Three-phase systems can be configured in two different ways to maintain equal loads; these are known as Delta and WYE configurations. The “Delta” and “WYE” names are specific indicators to the shapes that the wires resemble once connected to each other. “Delta” comes from the Greek symbol “Δ”, while “WYE” resembles the letter “Y” and is also known as the “star” circuit. Both, Delta and WYE configurations have the flexibility to deliver power over three wires, but the principal differences between the two are based on the number of wires available within each configuration and the current flow. The WYE configuration has gained popularity in recent years because it carries a neutral wire that allows both line-to-neutral (single-phase) and line-to-line (2/3 phase) connections.

What Are Three-Phase Power Line Filters?

Three-Phase EMI Filters are designed to meet the stringent requirements of EMC regulations for industrial applications. Regulations specify the maximum permissible noise levels (in dB) allowed back on power lines. The general requirements for a 3-Phase EMI filter design include input currents, line voltage, size limitation, and required insertion loss. In addition to this, the configuration of a 3-Phase EMI filter plays an important role in the design.

Three-Phase Delta vs. WYE Power Line Filters

Three-Phase Delta vs. WYE Power Line Filters Explained

Delta 3-Phase EMI Filter

Delta 3-Phase EMI Filters are designed to reduce the electromagnetic interference in devices connected to 3-phase delta power. The Delta configuration contains four wires; three hot conductors and one ground conductor. The phase loads (such as motor windings) are connected to each other in the shape of a triangle, where the connection is made from one end of winding to the starting end of the other, forming a closed circuit.

This power configuration does not have a neutral wire, but it can be fed by 3-phase WYE power if the neutral line is omitted/grounded. The delta system is used for power transmission because of the lower cost due to the absence of neutral cable. It is also used in applications requiring high starting torque.

Because of the absence of the neutral wire, capacitors used in Delta 3-phase EMI filters have to be rated for line-to-line (phase-to-phase) voltage which can increase the size, weight and cost. However, the absence of the neutral wire allows for higher current ratings than WYE and better performance in the same given cubic volume.

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Designing and Delta 3-Phase EMI Filter

  1. Locate the maximum power required by the load.
  2. Divide the maximum power required by the load by 3 to obtain the power per phase.
  3. Divide the answer by the line-to-line voltage.
  4. Multiply the previous answer by the square root of 3.

What Are the Advantages of Delta Configurations?

  • Delta configurations can typically be designed to handle higher current and are more efficient.
  • Protection for delta configurations can be simple.
  • Delta configurations are usually set up for the heavy-duty application and are preferable for power generation and power transmission.


WYE 3-Phase EMI Filter

WYE EMI Filters are designed to filter typical switch mode power conversion devices and other applications that require a neutral connection. This configuration is composed of five wires; three hot conductors, a neutral and a ground. In WYE configuration, the phase loads are connected at a single (neutral) point where the neutral wire gets connected.

When loads of a WYE configuration are fully balanced, no current flows through the neutral wire. When the loads are unbalanced, there is current through the neutral wire. This configuration allows the use of lower voltage capacitors (120VAC in 208VAC system and 277VAC in 480VAC system) in the filter, which can lead to savings in cost, weight, and volume.

In many applications, the neutral wire can be left floating. However, as previously mentioned, the WYE configuration provides the flexibility to connect the loads in the circuit either line-to-neutral or line-to-line. As opposed to Delta, this configuration can be used as a four-wire circuit or a five-wire circuit. WYE configurations are generally used in power distribution networks. It is primarily required in applications that call for less starting current and travel longer distances.

Designing and WYE 3-Phase EMI Filter

  1. Locate the maximum power required by the load.
  2. Divide the maximum power required by the load by 3 to obtain the power per phase.
  3. Divide the answer by line-to-neutral/ground voltage.

What Are the Advantages of WYE Configurations?

  • Preferred for power distribution because it can support single-phase (phase to neutral), 2-phase (phase-to-phase) and three-phase loads.
  • The star point is typically grounded which makes it great for unbalanced loads.
  • Less insulation is required for the same voltage support.

Cost of Three-Phase Power Line Filters Delta vs. WYE

A common question is whether Delta or WYE Three-Phase EMI Filters are more cost-effective. The Three-Phase Delta EMI Filter configuration can technically be more cost-effective than the WYE configurations because it only requires three-conductor cables instead of four, reducing the cost of materials to build the units. However, some of these cost-benefit can be offset by the need for high voltages rated components.

Astrodyne TDI Three-Phase EMI Filter Delta and WYE Configurations 

Astrodyne TDI offers 3-Phase EMI Filters in both Delta and WYE configurations to help reduce the electromagnetic interference in a variety of applications and ensure compliance with international emission standards. Our Three-Phase EMI filter ratings range from 480VAC/520VAC to 600 VAC, with current ratings of up to 2500A. Power line filters are offered in Single, Dual, and Multi-Stage designs, with higher current and voltage ratings available upon request.

With our extensive filter range and strong design capabilities, our team of engineers can guarantee to find the most effective Three-Phase EMI Filter solution to meet any specification and the most challenging applications.

Browse our selection of Three-Phase EMI Filters or contact our team to learn more about the product that will help meet your requirements.

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