SPD가 과전압으로부터 보호합니까? 네, 하지만 그 답변은 어떤 유형의 과전압이 관련되어 있는지에 따라 다릅니다. 서지 보호 장치(SPD)는 주로 과도 과전압을 제한하도록 설계되었으며, 일시적 과전압(TOV) 및 지속적 이상 전압은 다른 분석이 필요합니다.

"과전압 보호"라는 문구는 “overvoltage protection” 모든 과전압이 과도 서지는 아니기 때문에 오해의 소지가 있을 수 있습니다.

다음 세 가지 상황을 고려하십시오:

낙뢰로 인한 서지는 아주 짧은 순간 동안만 배전반에 도달합니다.

네트워크 결함으로 인해 공급 전압이 수 초 동안 크게 상승합니다.

또는 중성선이 느슨해지면 결함이 수리될 때까지 설비 일부에 비정상적인 전압이 지속됩니다.

이 세 가지 모두 다음을 포함하지만 과전압, 이들은 동일한 전기적 이벤트가 아닙니다.

그리고 서지 보호 장치(SPD)는 이들 모두에 동일하게 반응하지 않습니다.

가장 중요한 차이점은 다음과 같습니다.

일반적인 SPD는 기본적으로 과도 과전압을 제한하도록 설계되었습니다. 따라서 이를 일시적이거나 지속적인 비정상 공급 전압에 대한 보호 장치로 간주해서는 안 됩니다.

이러한 구분은 SPD 선정, 고장 분석, 심지어 엔지니어가 손상된 SPD를 해석하는 방식에도 영향을 미칩니다.

IEC 61643-01:2024 은 저압 SPD를 적어도 하나의 비선형 소자를 포함하며 다음을 목적으로 하는 장치로 정의합니다. 서지 전압을 제한하고 서지 전류를 분류(divert)하는 것. AC 저압 전력 시스템의 경우, 제품 요구 사항은 다음에 명시되어 있습니다. IEC 61643-11:2025.

빠른 답변: SPD가 과전압으로부터 보호합니까?

네, 하지만 특정 종류의 과전압에 대해서만 보호합니다.

SPD는 주로 다음을 위해 설계되었습니다. 과도 과전압, 낙뢰 효과나 스위칭 이벤트로 인해 발생하는 것과 같은.

일반적으로 공급 전압을 조정하거나 RMS 전압이 너무 높게 유지될 때 부하를 차단하기 위한 용도가 아닙니다.

아래 표는 기본적인 차이점을 보여줍니다.

이것이 바로 다음 질문이 나오는 이유입니다.

“내 배전반에 이미 SPD가 설치되어 있는가?”

이 질문은 다음 질문과 같지 않습니다.

“내 장비가 모든 비정상적인 전압 상태로부터 보호되고 있는가?”

그렇지 않습니다.

과도 서지 vs 일시적 과전압(TOV) vs 지속적 과전압

단어 과전압 광범위한 범주입니다.

어떤 보호 장치가 작동해야 할지 결정하기 전에 이벤트의 지속 시간과 원인을 파악하는 것이 필수적입니다.

1. 과도 과전압

과도 과전압은 단시간 동안 발생하는 전압 교란입니다.

일반적인 원인은 다음과 같습니다:

• 낙뢰 영향;
• 스위칭 동작;
• 유도성 부하 스위칭;
• 커패시터 스위칭;
• 전기 시스템 내의 기타 과도 현상.

표준 SPD 테스트는 일반적으로 다음과 같은 임펄스 파형을 사용합니다. 8/20 μs 전류 파형 Type 2 애플리케이션용.

이 이벤트는 매우 빠르게 발생합니다.

이것이 바로 SPD가 설계된 환경입니다. 클램핑 및 전류 분기 프로세스에 대해 더 자세히 검토하려면 다음 가이드를 참조하십시오. DC 서지 보호 장치의 작동 원리.

2. 일시적 과전압 — TOV

TOV는 다릅니다.

전압이 임펄스보다 훨씬 더 오래 높은 상태로 유지되며, 일반적으로 마이크로초 단위의 단일 서지보다는 전력 계통과 관련이 있습니다.

가능한 원인은 다음과 같습니다:

• 지락 사고;
• 중성선 문제;
• 계통 접지 상태;
• 철공진;
• 전압 조정 문제;
• 비정상적인 개폐 조건.

크기만으로는 위험을 정의할 수 없습니다.

전압 + 지속 시간 + 보호 모드 + 접지 시스템 + SPD 설계 모두 중요합니다.

예를 들어, ABB는 구분합니다. Uc, 최대 연속 동작 전압, 그리고 UT, 일시 과전압 내성. 이것의 OVR 실무 가이드 TOV 동작을 서지 전류 성능과 별도로 취급하며, 적용되는 스트레스가 SPD 연결 방식 및 네트워크 구성에 따라 달라짐을 보여줍니다.

지속적 또는 영구적 과전압

비정상적인 공급 전압이 일시적인 결함 이벤트처럼 작동하지 않고 지속될 경우, 엔지니어링 문제는 다시 변화합니다.

일반적인 병렬 연결형 SPD를 전압 조정기로 사용해서는 안 됩니다.

설계 목적이 다음과 같을 경우, 일반적으로 RMS 전압을 모니터링하고 차단을 시작하도록 설계된 장치가 필요합니다:

공급 전압이 허용 임계값 이상 또는 이하로 유지될 경우 부하를 차단합니다.

예를 들어, 슈나이더 일렉트릭(Schneider Electric) Harmony 전압 제어 계전기 과전압 및 저전압 모니터링 기능을 제공합니다. 이는 SPD의 고속 서지 방전 역할과는 다른 기능입니다.

Why Can an SPD Handle a Surge but Be Damaged by a TOV?

This seems contradictory at first.

An SPD may discharge a very large surge current measured in kiloamperes.

This is why asking “does an SPD protect against overvoltage?” requires first identifying whether the event is a transient surge, a TOV, or a sustained abnormal supply condition.

So why could a much smaller abnormal AC voltage damage it?

정답은 다음과 같습니다:

Energy is not determined by current magnitude alone. Time matters.

Consider an MOV-based SPD.

Under normal operating voltage, the MOV remains in a high-impedance state and conducts only a very small current.

When a transient surge raises the voltage sufficiently, the MOV becomes conductive.

Surge current is diverted through the SPD and the voltage is limited.

The surge then disappears very quickly.

The MOV returns toward its normal high-impedance state.

A simplified sequence looks like this:

That last condition is the problem.

If the voltage does not disappear quickly enough, the MOV may continue conducting.

Electrical energy then becomes heat.

In simplified form:

abnormal voltage → MOV current → power dissipation → temperature rise → disconnector operation or component damage

This is why:

40 kA Imax does not mean that an SPD can withstand any abnormal supply voltage.

Imax describes a defined surge-current capability.

TOV behavior describes a completely different type of electrical stress.

Uc, Up and TOV: Three Different Questions

Another common source of confusion is mixing voltage specifications together.

Suppose an SPD datasheet contains Uc, Up and a TOV/UT specification.

They should not be compared as though they describe the same thing.

The IEC definition of an SPD focuses on limiting surge voltage and diverting surge current. IEC 61643-12:2020 separately covers selection, operation, location and coordination principles for AC power SPDs. If the differences between Uc, Up, In, Imax and Iscpv are not yet clear, see our DC SPD 사양 가이드를 참조하십시오..

Does Higher Uc Mean Better TOV Protection?

Not automatically.

It is tempting to think:

Higher Uc = safer SPD.

이는 너무 단순한 해석입니다.

A suitably higher Uc can give more operating-voltage margin, but SPD selection involves a tradeoff.

The device must remain stable at the expected continuous system voltage while still providing an appropriate surge protection level.

NIST researchers have described this design dilemma for decades: an SPD must provide effective surge limitation without being expected to clamp longer-duration power-frequency overvoltages indefinitely.

따라서

Do not deliberately oversize Uc simply because you are worried about TOV.

Instead, check:

Real Case 1: A Documented TOV Above 150% Lasted About Four Seconds

This is where the distinction stops being theoretical.

A NIST-hosted paper by François Martzloff and Arshad Mansoor discusses actual power-system overvoltage scenarios.

One example cited from an EPRI report involved a power-system switching incident during restoration of power phase by phase.

The recorded condition produced an RMS voltage exceeding 150% of normal voltage for approximately four seconds.

The researchers identified the phenomenon as a temporary overvoltage associated with ferroresonance.

Notice what makes this different from a normal SPD surge event:

Four seconds may sound short to a person.

For an MOV that is dissipating abnormal power continuously, it is extremely long compared with a microsecond-scale surge.

Real Case 2: Commercial SPDs Were Tested Under Simulated TOV Conditions

Another NIST-hosted TOV study by researchers from Eaton Electrical, EPRI Solutions and François Martzloff investigated what happens when commercial SPDs experience several TOV conditions.

The study intentionally exposed commercial devices to conditions representing real power-system abnormalities.

The test program included the following examples:

The values relate to the study’s 120 V system basis; they must not be copied directly as ratings for another SPD or another electrical system.

The result was especially important.

The researchers found that SPD response varied substantially depending on the product design.

The three cord-connected SPD specimens failed under the simulated 1.5 pu neutral-loss condition, while the two permanently connected specimens used in that study survived the first four test scenarios. Under the extreme 3.0 pu test, the permanently connected specimens experienced partial internal failure but retained some protective capability.

This should not be interpreted as:

“Hardwired SPDs always survive TOV.”

The study used only a small group of specific products and represents historical designs.

Its real lesson is more useful:

Two products with similar-looking surge ratings may behave very differently under a long-duration abnormal voltage condition.

That is why TOV cannot be judged from Imax alone.

Does an SPD Protect Against Overvoltage Caused by Neutral Loss?

Neutral interruption is one of the most useful examples because it explains why the phrase “the SPD should clamp the voltage” can become dangerous.

In a multi-wire system with unequal phase-to-neutral loads, loss of the neutral can shift the neutral point.

The voltage across individual loads can then become severely unbalanced.

NIST describes loss-of-neutral conditions in North American 120/240 V three-wire systems where one side can approach twice normal voltage depending on the connected load impedances. The paper notes that such neutral problems may result from loose connections, mechanical damage or corrosion.

Now imagine an MOV-based SPD connected across the affected conductors.

If the abnormal power-frequency voltage pushes the MOV into conduction:

it begins conducting continuously.

But an MOV is not supposed to behave like a voltage regulator carrying that current indefinitely.

It may heat rapidly.

Eventually the result may be:

The last point is particularly important.

A typical parallel-connected SPD can disconnect itself while the protected circuit remains energized.

따라서

SPD failure or disconnection does not necessarily remove the abnormal voltage from the load.

A conventional SPD should therefore not be relied on as the sole protection against neutral-loss overvoltage. Where the design requires abnormal RMS voltage to be detected and the load disconnected, a dedicated voltage-monitoring or protection function may be needed. The neutral fault itself must still be located and corrected.

Why Doesn’t the SPD Simply Clamp the TOV?

Because doing so could require the SPD to absorb or divert power continuously.

Consider a simplified example.

A Type 2 MOV-based SPD is installed across the supply.

A brief transient occurs.

The MOV conducts for a very short time and then stops.

That is normal.

Now assume abnormal mains voltage remains high for many seconds.

If the MOV attempts to hold the voltage down continuously, the SPD essentially becomes part of a power-frequency current path.

The longer the current flows, the greater the thermal stress.

That can lead to:

thermal runaway → disconnector operation → loss of SPD protection or component damage

This is exactly why SPDs require coordinated fault and disconnection behavior rather than simply “clamping everything.”

TOV Withstand Does Not Mean TOV Protection for the Load

This distinction is extremely important when reading datasheets.

Suppose a manufacturer states that an SPD has a certain UT or TOV capability.

That generally describes the SPD’s behavior under specified test conditions.

It does not automatically mean:

“The downstream equipment will remain at normal voltage throughout the TOV.”

These are different functions.

Compare them:

Schneider’s Harmony control relays, for example, monitor overvoltage and undervoltage conditions with threshold and timing functions; this is fundamentally different from the shunt surge-diversion function of an SPD.

Can a Circuit Breaker Protect Against Overvoltage?

A standard circuit breaker should not automatically be treated as an overvoltage protector either.

Its primary job is overcurrent protection.

If voltage rises while load current remains below the breaker trip characteristic, an ordinary breaker may remain closed.

That means four devices can perform four different functions:

This is why replacing one device with another based only on the word “protection” is a mistake. For the separate question of SPD overcurrent coordination, see our guide to SPD backup fuse and circuit-breaker selection.

Can a Bigger kA SPD Solve a TOV Problem?

아니요.

Suppose one SPD is rated:

In = 20 kA
Imax = 40 kA

and another says:

Imax = 60 kA

The 60 kA product is not automatically better at surviving a temporary power-frequency overvoltage.

The ratings describe different stresses.

Therefore, if SPDs repeatedly fail without obvious lightning activity, simply purchasing a higher-Imax model may not solve the actual problem.

Repeated SPD Failure: What Should You Investigate?

This is a situation where field diagnosis matters more than changing brands.

Use this investigation table.

NIST’s historical analysis lists power-system faults, poor voltage regulation, conductor problems, generator conditions, ferroresonance and loss of neutral among conditions capable of contributing to SPD overvoltage stress. If a device already shows a red indicator, abnormal heating or visible damage, our guide on SPD 불량 여부 확인 방법 explains the next inspection steps.

What About TOV in Solar PV DC Systems?

Extra care is required here.

Most discussion of power-frequency TOV relates to AC systems.

A PV DC system has different operating conditions.

Important PV DC concerns include:

IEC 61643-31:2018 specifically covers SPDs intended for the DC side of PV installations up to 1500V DC. IEC 61643-41:2025 now covers general DC low-voltage SPDs up to 1500 V DC, but it explicitly excludes PV applications, which remain within IEC 61643-31.

Therefore, do not take an AC TOV number from a 230/400 V AC SPD datasheet and assume the same rule applies to a 1000 V or 1500 V PV SPD.

For PV systems, check the exact:

Ucpv + topology + protection mode + manufacturer documentation + applicable PV SPD standard.

For voltage selection, see our DC SPD voltage selection guide. For grounded versus floating PV arrangements and protection paths, see 2P vs 3P DC SPD for Solar PV.

AC SPD vs PV DC SPD Under Overvoltage

This is another reason AC and DC SPDs should not be interchanged casually.

IEC currently lists IEC 61643-11:2025 for AC low-voltage SPDs, while IEC 61643-31:2018 addresses PV DC SPDs. For a practical explanation of why an AC-only SPD should not simply be moved to a DC circuit, see What Happens If You Use an AC SPD on a DC System?.

Common Mistakes About SPD and Overvoltage

How to Select an SPD When TOV Is a Concern

Instead of starting with:

“How many kA do I need?”

start with the electrical system.

Installation also matters after the product is selected. Long SPD connecting conductors can increase the voltage appearing at the protected equipment during a fast surge; see our guide to SPD distance from the inverter and SPD lead length.

This order avoids a common purchasing mistake:

choosing the largest kA number first and checking voltage compatibility later.

Practical Example: Diagnosing an SPD That Keeps Failing

Assume an electrician installs a new Type 2 SPD.

A few days later the status window indicates replacement.

A new cartridge is installed.

It fails again.

It would be easy to conclude:

“The SPD quality is poor.”

But that is only one possibility.

A better troubleshooting sequence is:

Only after these checks should repeated SPD replacement be treated as a simple product issue.

SPD vs Overvoltage Relay: Do You Need Both?

In some installations, yes.

They solve different problems.

Think of them this way:

SPD:
“What happens if a very fast surge arrives?”

Voltage monitoring protection:
“What happens if the supply voltage remains abnormal?”

A system containing both functions may therefore provide broader protection than either one alone.

But the exact protection design depends on the installation, applicable codes and equipment requirements.

SPD Overvoltage Protection Checklist

Before approving an SPD specification, confirm the following:

자주 묻는 질문

Does an SPD Protect Against Overvoltage or High Voltage?

An SPD primarily protects against transient overvoltage, such as short-duration surges caused by lightning effects or switching events. It should not automatically be treated as protection against every temporary or sustained abnormal supply voltage. If the supply voltage remains excessively high, separate voltage monitoring or disconnection protection may be required.

Can an SPD protect against temporary overvoltage?

It depends on the SPD and the specific TOV condition.

The datasheet or manufacturer documentation may specify TOV withstand or behavior for defined voltage, duration and connection conditions.

Do not assume that every SPD will survive every TOV.

What happens if mains voltage stays above the SPD’s Uc?

The result depends on how far the voltage exceeds Uc, how long it lasts and the SPD design.

In an MOV-based SPD, excessive continuous voltage can increase MOV current and heating.

This may eventually cause thermal disconnection or damage.

Is TOV the same as a lightning surge?

아니요.

A lightning-related surge is a short transient event.

A TOV lasts much longer and is usually associated with a power-system abnormality.

The stresses placed on an SPD are therefore very different.

Does Imax tell me the TOV capability?

아니요.

Imax is a surge-current parameter.

TOV behavior must be evaluated separately.

Does a 40 kA SPD protect against a 400 V overvoltage?

That question cannot be answered from 40 kA.

You need to know the nominal system voltage, Uc, connection mode, TOV declaration, duration of the abnormal voltage and the SPD design.

Can an SPD prevent damage from a broken neutral?

Do not rely on an SPD alone.

A broken or displaced neutral can create dangerous abnormal phase-to-neutral voltages.

Neutral integrity must be restored, and where required a dedicated voltage-monitoring and disconnection function should be used.

Can a circuit breaker replace an SPD?

아니요.

A conventional circuit breaker protects primarily against overcurrent and short circuit.

An SPD limits transient overvoltage.

They perform different functions.

Can an overvoltage relay replace an SPD?

아니요.

A voltage-monitoring relay can detect abnormal RMS voltage and initiate a switching action.

It does not replace the high-speed surge-diversion function of an SPD.

결론

그래서, does an SPD protect against overvoltage?

The technically correct answer is:

An SPD protects against transient overvoltage, but it should not be treated as universal protection against every temporary or sustained abnormal voltage condition.

Surge current ratings such as In, Imax and Iimp describe transient performance.

Uc/Ucpv describes continuous voltage compatibility.

Up describes surge-voltage limitation.

And TOV behavior describes how the SPD responds to a specified temporary abnormal-voltage condition.

These parameters should never be treated as interchangeable.

Real-world research also shows why the distinction matters. NIST/EPRI investigations found dramatically different SPD responses to temporary-overvoltage conditions, ranging from survival to internal failure depending on the device and the applied stress.

The practical rule is simple:

First identify the electrical event. Then select the protection function.

Use an SPD for transient surge protection.

Use appropriate voltage monitoring or disconnection when persistent abnormal supply voltage must be detected and removed.

And if SPDs repeatedly fail, investigate system voltage, neutral condition, earthing, Uc/Ucpv and TOV conditions before simply replacing the module again.

For PV applications, always verify the exact SPD model against the system’s maximum DC voltage, PV topology and applicable IEC 61643-31 requirements.