Transcript

Introduction

Hi, everyone. Welcome to today’s Ask a Pro session. I’m Bryan Western from PMI, and today I’m gonna be talking about the difference between voltage regulation and voltage stability. In this presentation, we’ll cover voltage regulation and the factors affecting it, and we’ll also cover voltage stability, some applicable standards, as well as voltage regulation reports in PQ Canvass.

Voltage Regulation vs. Voltage Stability

Voltage regulation and voltage stability, they’re not the same thing. They are related, but they’re not the same thing. Voltage regulation is kind of like keeping your room at a comfortable temperature. It’s local. And voltage stability is more of a system-wide issue, and it’s how the system as a whole responds to stress.

Voltage regulation can be measured easily using power quality devices. Whereas stability is not diagnosable by power quality measurements alone, but some of the indirect symptoms can be observed.

What Is Voltage Regulation?

Voltage regulation is the power company’s job of keeping the voltage constant. They measure voltage in your home and make sure it stays within safe limits. When you turn on more things, like if you plug in a microwave, that changes what your home needs, and the system automatically adjusts so the voltage will stay steady.

And it’s observable, meaning you go out, you can measure it with an instrument. It’s also steady state, meaning we’re looking at normal, everyday conditions, not emergency situations.

Why Should You Care?

Let’s talk about what happens when voltage regulation goes wrong. Let’s say you have a computer and it’s designed to run on a steady 120 volts. If the voltage gets too high, say 150 volts, you could permanently damage the computer. If it drops too low, like say 90 volts, your computer might shut off to protect itself.

And for bigger machines, like motors that run factory equipment or large electric motors, when voltage drops, the motor has to work harder and draw more current to do the same job. And that can lead to the motor overheating, or burning out, or special protective switches kick in to shut it down. Good voltage regulation will mean that your equipment lasts longer, works reliably, and doesn’t unexpectedly shut off in the middle of something important.

ANSI C84.1 Standard

So how do engineers decide what the right voltage is? There’s actually a standard. It’s called ANSI C84.1, and that standard says that the voltage has gotta stay between 95 and 105% of the IDL voltage. That’s called preferred range. And there’s also a slightly looser range, range B, between 91 and 105%. That’s the acceptable range, but it’s not ideal.

These standards apply to normal, everyday conditions. It’s not applicable for emergencies or sudden outages. It’s about sustained voltage, meaning steady voltage over time. But these standards only talk about steady conditions. It’s not sudden events like lightning strikes or a power plant suddenly goes offline.

Factors Affecting Voltage Regulation

So what affects whether your voltage is steady? A bunch of things, actually.

• First, there’s distance. If you live far from a power plant, electricity has to travel through long wires, and those wires have resistance. So the farther away, the more the voltage will drop along the way.
• Second, how many things are you running? Everyone in your neighborhood all at once on a hot day, touching their air conditioning on, there’s gonna be huge demand. So the system has to adjust for that load.
• Third, power companies have special transformers with changeable taps that can bump the voltage up and down. Power companies add capacitor banks also, and that can help with reactive power, which basically keeps the system stable.

All these things change constantly throughout the day as usage goes up and down, and the system has to keep adjusting to keep voltages stable. Substations have transformers with, like I said earlier, the tap changers. They adjust throughout the day, and these are actively adjusted as the demand changes throughout the day.

Measuring Voltage Regulation

Now, if your job is to check whether voltage regulation is good, whether it’s staying within the standards we talked about earlier, how would you do that? You’d use a power quality monitor to collect that data. In this case, it’d be voltage. Then in PQ Canvass, you enter a few bits of information about how the monitor was hooked up, and you can then generate a compliance report, which will compare the collected data with those applicable standards.

Voltage Stability

Stability is a bigger picture issue. It’s an electrical system’s ability to bounce back after a disturbance. And this is a system-wide property.

When voltage stability works, the system has enough reactive power to meet demand. The electricity will flow smoothly, and if there’s a disruption, the system will recover. When things go wrong and exceeds what the system can actually supply, voltage collapse can happen. The voltage starts dropping, and as it drops, it actually demands more reactive power, which makes things worse. It’s kind of a downhill spiral.

The main solution for this is to increase reactive power support. You can add more capacitor banks, devices that provide reactive power. They can also add sophisticated devices, SVCs or SACCOMs, and these are basically electronic devices that inject reactive power to support the system.

Analyzing Voltage Stability

So when engineers need to actually figure out if a system is stable, how do they do that? One method is static analysis. They can generate graphs. Imagine a map that shows the relationship between power being delivered and voltage. They would look at the critical point on the map, a point where, if anything just slightly goes wrong, voltage collapse could happen. That gives them margin, which is how much room do we have before a disaster, basically.

They can use computer models of the entire transmission system. They ask what-if questions. These questions would be, for example, what if the power plant goes offline? What if the load increases? And they look at these scenarios and see if the system can handle it.

And there’s also dynamic analysis, which looks at how the system responds over time second by second as problems develop. All of these require serious engineering, and computer models, and system-wide data. It’s not something that you can measure locally. It’s not something that local measurements alone can solve, so it’s a system-wide issue. And that’s kind of like the job of system operators and transmission engineers.

Recap

So just to recap, regulation and stability. Regulation’s a very local thing. It’s something you can measure with devices, and it’s a steady state phenomena as well. And stability is a system-wide, basically a survivability property.

Appreciate everyone’s time. If you have any questions, you can always feel free to call in or send us an email. Have a good weekend.