Explain PSM and TSM related to protective relays.
2 Answers
### PSM (Plug Setting Multiplier) and TSM (Time Setting Multiplier) in Protective Relays
In protective relays, **PSM (Plug Setting Multiplier)** and **TSM (Time Setting Multiplier)** are critical parameters used to determine the operation of overcurrent relays. These relays help protect electrical systems from faults like short circuits or overloads by disconnecting faulty parts of the system. Let’s break down both terms in detail.
---
### 1. **Plug Setting Multiplier (PSM)**
The **Plug Setting Multiplier (PSM)** indicates how much the actual current exceeds the relay’s set current value. It determines how sensitive the relay is to overcurrents.
#### **Formula**:
\[
\text{PSM} = \frac{\text{Fault Current}}{\text{Relay Current Setting}}
\]
#### **Explanation**:
- **Fault Current**: The actual current flowing through the system during a fault condition.
- **Relay Current Setting**: This is the set current at which the relay is configured to operate.
For example, if the relay is set to trip at 10 A, and the fault current is 50 A, then the **PSM** would be:
\[
\text{PSM} = \frac{50 \, \text{A}}{10 \, \text{A}} = 5
\]
This means the fault current is 5 times the set current, and the relay will respond more quickly because the higher the PSM, the faster the relay tends to operate.
#### **Importance**:
- **Higher PSM**: Indicates a higher fault current compared to the relay's setting, meaning the fault is more severe, and the relay must operate faster.
- **Lower PSM**: Indicates the current is closer to the setting, meaning the fault might be less severe, and the relay operation can be slower.
---
### 2. **Time Setting Multiplier (TSM)**
The **Time Setting Multiplier (TSM)** is a factor that adjusts the operating time of the relay, depending on the level of fault current. It modifies the time delay before the relay trips in an inverse time overcurrent relay (IDMT).
#### **Explanation**:
The relay’s operating time is inversely proportional to the fault current. The **higher the fault current**, the **faster** the relay operates. However, to fine-tune the tripping time, the **TSM** is applied.
- The TSM is usually expressed as a percentage or decimal. For instance, if the TSM is 0.2 or 20%, the relay will operate at 20% of its full-time delay.
#### **Operating Time Formula**:
\[
\text{Operating Time} = \text{Standard Operating Time} \times \text{TSM}
\]
For example:
- If the relay’s standard operating time (without TSM) for a fault with a PSM of 5 is 3 seconds, and the TSM is set to 0.5, the relay will operate in:
\[
\text{Operating Time} = 3 \, \text{seconds} \times 0.5 = 1.5 \, \text{seconds}
\]
Thus, the relay will trip faster based on the TSM setting.
#### **Importance**:
- **Lower TSM (e.g., 0.1 or 10%)**: Reduces the tripping time, meaning the relay will trip faster for the same PSM.
- **Higher TSM (e.g., 1 or 100%)**: Increases the tripping time, meaning the relay will trip slower.
---
### **Combined Operation of PSM and TSM in Protective Relays**
In most overcurrent protective relays (particularly **IDMT** relays), both PSM and TSM work together to determine how and when the relay will operate. The relationship is as follows:
- **PSM** determines the severity of the fault (how much the fault current exceeds the set current).
- **TSM** adjusts the time delay based on the severity (how fast or slow the relay should operate).
The time-current characteristic curve of an IDMT relay is defined by the combination of PSM and TSM. This curve shows that:
- For **higher PSM values**, the relay operates quickly.
- The **TSM adjusts** this time to ensure proper coordination with other relays in the system.
### **Example**:
1. A relay is set to operate at 20 A, and a fault occurs at 100 A. The PSM is:
\[
\text{PSM} = \frac{100}{20} = 5
\]
So, the fault current is 5 times the set current.
2. Without TSM, the relay might be set to operate in 2 seconds for this PSM. If the TSM is set to 0.6, the actual operating time will be:
\[
\text{Operating Time} = 2 \, \text{seconds} \times 0.6 = 1.2 \, \text{seconds}
\]
Hence, the relay trips in 1.2 seconds instead of 2 seconds due to the TSM setting.
---
### **Summary**:
- **PSM** controls how much the actual current exceeds the set current in the relay, giving a sense of how severe the fault is.
- **TSM** adjusts the time the relay takes to trip based on the severity of the fault, ensuring the relay trips faster for higher fault currents and slower for lower fault currents.
Together, PSM and TSM ensure that the relay operates accurately and timely, providing essential protection to the electrical system against overcurrent situations while coordinating with other protection devices in the network.
In protective relays, **PSM (Plug Setting Multiplier)** and **TSM (Time Setting Multiplier)** are critical parameters used to determine the operation of overcurrent relays. These relays help protect electrical systems from faults like short circuits or overloads by disconnecting faulty parts of the system. Let’s break down both terms in detail.
---
### 1. **Plug Setting Multiplier (PSM)**
The **Plug Setting Multiplier (PSM)** indicates how much the actual current exceeds the relay’s set current value. It determines how sensitive the relay is to overcurrents.
#### **Formula**:
\[
\text{PSM} = \frac{\text{Fault Current}}{\text{Relay Current Setting}}
\]
#### **Explanation**:
- **Fault Current**: The actual current flowing through the system during a fault condition.
- **Relay Current Setting**: This is the set current at which the relay is configured to operate.
For example, if the relay is set to trip at 10 A, and the fault current is 50 A, then the **PSM** would be:
\[
\text{PSM} = \frac{50 \, \text{A}}{10 \, \text{A}} = 5
\]
This means the fault current is 5 times the set current, and the relay will respond more quickly because the higher the PSM, the faster the relay tends to operate.
#### **Importance**:
- **Higher PSM**: Indicates a higher fault current compared to the relay's setting, meaning the fault is more severe, and the relay must operate faster.
- **Lower PSM**: Indicates the current is closer to the setting, meaning the fault might be less severe, and the relay operation can be slower.
---
### 2. **Time Setting Multiplier (TSM)**
The **Time Setting Multiplier (TSM)** is a factor that adjusts the operating time of the relay, depending on the level of fault current. It modifies the time delay before the relay trips in an inverse time overcurrent relay (IDMT).
#### **Explanation**:
The relay’s operating time is inversely proportional to the fault current. The **higher the fault current**, the **faster** the relay operates. However, to fine-tune the tripping time, the **TSM** is applied.
- The TSM is usually expressed as a percentage or decimal. For instance, if the TSM is 0.2 or 20%, the relay will operate at 20% of its full-time delay.
#### **Operating Time Formula**:
\[
\text{Operating Time} = \text{Standard Operating Time} \times \text{TSM}
\]
For example:
- If the relay’s standard operating time (without TSM) for a fault with a PSM of 5 is 3 seconds, and the TSM is set to 0.5, the relay will operate in:
\[
\text{Operating Time} = 3 \, \text{seconds} \times 0.5 = 1.5 \, \text{seconds}
\]
Thus, the relay will trip faster based on the TSM setting.
#### **Importance**:
- **Lower TSM (e.g., 0.1 or 10%)**: Reduces the tripping time, meaning the relay will trip faster for the same PSM.
- **Higher TSM (e.g., 1 or 100%)**: Increases the tripping time, meaning the relay will trip slower.
---
### **Combined Operation of PSM and TSM in Protective Relays**
In most overcurrent protective relays (particularly **IDMT** relays), both PSM and TSM work together to determine how and when the relay will operate. The relationship is as follows:
- **PSM** determines the severity of the fault (how much the fault current exceeds the set current).
- **TSM** adjusts the time delay based on the severity (how fast or slow the relay should operate).
The time-current characteristic curve of an IDMT relay is defined by the combination of PSM and TSM. This curve shows that:
- For **higher PSM values**, the relay operates quickly.
- The **TSM adjusts** this time to ensure proper coordination with other relays in the system.
### **Example**:
1. A relay is set to operate at 20 A, and a fault occurs at 100 A. The PSM is:
\[
\text{PSM} = \frac{100}{20} = 5
\]
So, the fault current is 5 times the set current.
2. Without TSM, the relay might be set to operate in 2 seconds for this PSM. If the TSM is set to 0.6, the actual operating time will be:
\[
\text{Operating Time} = 2 \, \text{seconds} \times 0.6 = 1.2 \, \text{seconds}
\]
Hence, the relay trips in 1.2 seconds instead of 2 seconds due to the TSM setting.
---
### **Summary**:
- **PSM** controls how much the actual current exceeds the set current in the relay, giving a sense of how severe the fault is.
- **TSM** adjusts the time the relay takes to trip based on the severity of the fault, ensuring the relay trips faster for higher fault currents and slower for lower fault currents.
Together, PSM and TSM ensure that the relay operates accurately and timely, providing essential protection to the electrical system against overcurrent situations while coordinating with other protection devices in the network.