The #1 priority of any design involving electricity should be user safety.
Using an electrical switchgear is a necessity to handle larger voltages and currents safely. But you need to use the right electrical switchgear parts to ensure predictable performance and reliability.
The six design considerations below apply across all manufacturing processes for electrical switchgear design. However, many can be best achieved with powder metallurgy.
Design Considerations for Electrical Switchgear Parts
Solenoids and relays have the same basic function in that an electric current or signal causes a contact to close thus activating the electric device. However, the differences between relays and solenoids are quite important. Specifically, solenoids are almost exclusively in DC devices and the electrical contactor is at the end of the solenoid armature shaft. Using an AC current will disengage the contactor during parts of the AC cycle, resulting in interrupted operation.
A good example of a solenoid is the automobile starter; when you engage the starter motor the solenoid collapses the spring and engages the gear on the end of the starter motor shaft with the flywheel of the engine.
Relays, on the other hand, offer remote control of the device; implying, that no part of the relay material or coil contacts the circuit voltage or current. This remote-control feature enables smaller currents in the relay to effectively control much larger currents or voltage. Relays can also operate on AC or DC voltages. AC operated relays require laminations to minimize eddy current heating effects.
A concern in relays is often the “bounce” (make and break of the current) with the initial engagement of the relay. Bounce can be a problem with AC designs because of the current going to zero during the voltage reversal phase of the AC cycle. In high-speed applications, this is a no-no. In many relay designs, a DC power supply is incorporated to operate the relay, eliminating or minimizing bounce.
Obviously, sintered powder metallurgy materials are best suited for DC operated relays (because of the eddy current heating effect). The speed and force of the relay can be controlled by choice of the soft magnetic material (specifically related to the permeability, coercive force and induction) and the number of turns of the copper wire in the relay material.
What Do You Need From an Electrical Switchgear?
With electrical switchgear design, you need to prepare for extreme-use situations. You have to make a switch that will stand up to significant voltage and currents – and that you can slam in at a moment’s notice without worrying that the structure will fail.
The operator (hopefully) is in a remote location from the reaction point. You want something that turns on and off quickly without needing to watch over it or worry.
How do you design for these demands? Electrical switchgear components need to meet certain criteria, including:
- 3D design
- Scrap waste
1. High Hardness
You can prevent a lot of electrical switchgear failures just by having sufficient hardness in your components. A switchgear component with good mechanical properties will hold up to the continual engaging and disengaging of the switchgear relay. Without sufficient hardness, the part may deform at the end and may not operate correctly.
Today, advanced powder metallurgy sintering and the alloy options possible with powder metal can help achieve this hardness. But which materials will get you there most easily?
You’ll want to avoid pure iron because it’s comparatively soft in the world of metal. Even the usefulness of iron-phosphorus is on the fence. Iron-silicon, however, is a solid option frequently used in powder metal parts -- and you won’t lose the electrical characteristics you need! The ability to combine electrical and mechanical properties makes powder metallurgy (PM) an attractive option here.
2. Good Permeability
You want strong electrical properties, which means you want high permeability because it relates to fast response for both engagement and disengagement.
Recent work by advanced powder metallurgy companies shows that now you can get permeability of 7,000+ with iron-silicon material. The great thing about using iron-silicon in an electric motor switchgear is that it responds better in DC applications than iron-phosphorus counterparts. You also gain the benefit of solid impact resistance.
3. Low Resistance
Resistance in electrical applications leads to heat accumulation – both a performance issue and a safety issue. Good alloying systems available with powder metal can deliver low-resistivity parts for electrical switchgear suppliers. Iron-silicon parts is once again a prime example of a material with low resistivity.
You’ll need high-temperature sintering -- at least 2300°F, but ultra-high-temperature sintering in excess of 2400° is preferable -- to produce iron-silicon powder metal components. Taking your part the extra mile in the furnace is often worth it.
4. Corrosion Resistance
Corrosion is a necessary consideration in electrical equipment design; fortunately you can do a lot to limit it. Corrosion is costly, requiring repairs and replacements earlier than you’d like.
Your switchgears may be subjected to:
- High temperatures
- Other extreme conditions
Why not protect them the best you can? Iron-silicon components have the advantage of being naturally corrosion-resistant because it forms a silicon oxide layer.
5. Design in 3D
Most switchgears are stacked components made of lamination and electrical steel. This old-school process is done in 2D, which limits you design-wise.
What if you could design in 3D? Because it involves making parts from scratch, the powder metallurgy process makes complex shape-making possible. Your part can come out whole, practically ready to use, instead of requiring extra processing to achieve the shape you want.
6. Limit Waste
The scrap waste of the steel lamination process is high. That’s because you have to take multiple sheets and size them to fit. Your manufacturer must make cut after cut to fabricate the curve you require. This leads to extensive waste in the production process.
One of the advantages of powder metallurgy manufacturing is that it's like sculpting clay -- you use it as you see fit. While it can be a little more labor-intensive on the front end as your contractor prepares for production, the process results in far less waste than lamination does.
Using PM processes inherently limits scrap waste. This is one of the main attractions of using powder metal, and it applies to switchgear design just as it applies to auto motors.
The PM Advantage Explained
Electrical switchgear manufacturers who follow these six pieces of advice will create a safer, more capable piece of equipment.
While many of these tips are universal to all manufacturing processes, some of them are ideal for powder metallurgy services. If you have additional questions about whether PM fits into your switchgear design, just ask!