Power Systems Protection and Relaying code numbers

In North America protective relays are generally referred to by standard device numbers. Letters

are sometimes added to specify the application (IEEE Standard C37.2-2008).

Following the ANSI/IEEE Standard Device Numbers (the more commonly used ones are in bold)

1 - Master Element
2 - Time Delay Starting or Closing Relay
3 - Checking or Interlocking Relay
4 - Master Contactor
5 - Stopping Device
6 - Starting Circuit Breaker
7 – Rate of Change Relay
8 - Control Power Disconnecting Device
9 - Reversing Device
10 - Unit Sequence Switch
11 – Multifunction Device
12 - Overspeed Device
13 - Synchronous-speed Device
14 - Underspeed Device
15 - Speed or Frequency-Matching Device
16 – Data Communications Device
20 - Elect. operated valve (solenoid valve)
21 - Distance Relay
23 - Temperature Control Device
24 – Volts per Hertz Relay
25 - Synchronizing or Synchronism-Check Device
26 - Apparatus Thermal Device
27 - Undervoltage Relay
30 - Annunciator Relay
32 - Directional Power Relay
36 - Polarity or Polarizing Voltage Devices
37 - Undercurrent or Underpower Relay
38 - Bearing Protective Device
39 - Mechanical Conduction Monitor
40 –Field (over/under excitation) Relay
41 - Field Circuit Breaker
42 - Running Circuit Breaker
43 - Manual Transfer or Selector Device
46 – Rev. phase or Phase-Bal. Current Relay
47 - Phase-Seq. or Phase-Bal. Voltage Relay
48 - Incomplete-Sequence Relay
49 - Machine or Transformer Thermal Relay
50 - Instantaneous Overcurrent
51 - AC Time Overcurrent Relay
52 - AC Circuit Breaker
53 – Field Excitation Relay
55 - Power Factor Relay
56 - Field Application Relay
59 - Overvoltage Relay
60 - Voltage or Current Balance Relay
62 - Time-Delay Stopping or Opening Relay
63 - Pressure Switch
64 - Ground Detector Relay
65 - Governor
66 – Notching or jogging device
67 - AC Directional Overcurrent Relay
68 - Blocking or “out of step” Relay
69 - Permissive Control Device
74 - Alarm Relay
75 - Position Changing Mechanism
76 - DC Overcurrent Relay
78 - Phase-Angle Measuring Relay
79 - AC-Reclosing Relay
81 - Frequency Relay
83 - Automatic Selective Control or Transfer Relay
84 - Operating Mechanism
85 – Pliot Communications, Carrier or Pilot-Wire Relay
86 - Lockout Relay
87 - Differential Protective Relay
89 - Line Switch
90 - Regulating Device
91 - Voltage Directional Relay
92 - Voltage and Power Directional Relay
94 - Tripping or Trip-Free Relay
B – Bus
F - Field
G – Ground or generator
N – Neutral
T – Transformer

What is Engine Cycle ?

The term "engine cycle" typically refers to the sequence of events that occur within an internal combustion engine during one complete operation. There are several types of engine cycles, but the most common ones are the Otto cycle and the Diesel cycle.

1. Otto Cycle: This is the cycle used in gasoline engines. It consists of four strokes:

   • Intake Stroke: The intake valve opens, allowing the air-fuel mixture to enter the combustion chamber as the piston moves down.
   • Compression Stroke: Both intake and exhaust valves close, and the piston moves up, compressing the air-fuel mixture.
   • Power Stroke: When the air-fuel mixture is compressed, a spark plug ignites it, causing an explosion that drives the piston down, producing power.
   • Exhaust Stroke: Finally, the exhaust valve opens, and the piston moves up, pushing the burnt gases out of the combustion chamber.

2. Diesel Cycle: This cycle is used in diesel engines and is similar to the Otto cycle but differs in the method of ignition. It also consists of four strokes:

   • Intake Stroke: The intake valve opens, allowing air into the cylinder.
   • Compression Stroke: The air is compressed highly, raising its temperature. Fuel is then injected directly into the cylinder near the top of the compression stroke.
   • Power Stroke: The injected fuel ignites due to the high temperature of the compressed air, driving the piston down.
   • Exhaust Stroke: The exhaust valve opens, and the piston moves up, expelling the exhaust gases.

These cycles are fundamental to the operation of internal combustion engines and are the basis for the efficiency and performance characteristics of various engine designs.