Exhibit 31.2

 

**Certifications**

 

 
|   | I, Donald Tremblay, certify that:                                                                                                                                                                                                                                                                                                                                       |
|--------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
|   |                                                                                                                                                                                                                                                                                                                                                                    |
| 1.     | I have reviewed this   annual report on Form 40-F of TransAlta Corporation;                                                                                                                                                                                                                                                                                        |
|   |                                                                                                                                                                                                                                                                                                                                                                    |
| 2.     | Based on my knowledge,   this report does not contain any untrue statement of a material fact or omit   to state a material fact necessary to make the statements made, in light of   the circumstances under which such statements were made, not misleading with   respect to the period covered by this report;                                                      |
|   |                                                                                                                                                                                                                                                                                                                                                                    |
| 3.     | Based on my knowledge,   the financial statements, and other financial information included in this   report, fairly present in all material respects the financial condition,   results of operations and cash flows of the issuer as of, and for, the   periods presented in this report;                                                                             |
|   |                                                                                                                                                                                                                                                                                                                                                                    |
| 4.     | The issuer’s other   certifying officer(s) and I are responsible for establishing and   maintaining disclosure controls and procedures (as defined in Exchange Act   Rules 13a-15(e) and 15d-15(e)) and internal control over financial   reporting (as defined in Exchange Act Rules 13a-15(f) and   15d-15(f)) for the issuer and have: |
|   |                                                                                                                                                                                                                                                                                                                                                                    |
|   | a)                                                                                                                                                                                                                                                                                                                                                                      | Designed such   disclosure controls and procedures, or caused such disclosure controls and   procedures to be designed under our supervision, to ensure that material   information relating to the issuer, including its consolidated subsidiaries,   is made known to us by others within those entities, particularly during the   period in which this report is being prepared; |
|   |                                                                                                                                                                                                                                                                                                                                                                    |   |
|   | b)                                                                                                                                                                                                                                                                                                                                                                      | Designed such internal   control over financial reporting, or caused such internal control over   financial reporting to be designed under our supervision, to provide   reasonable assurance regarding the reliability of financial reporting and the   preparation of financial statements for external purposes in accordance with   generally accepted accounting principles; |
|   |                                                                                                                                                                                                                                                                                                                                                                    |   |
|   | c)                                                                                                                                                                                                                                                                                                                                                                      | Evaluated the   effectiveness of the issuer’s disclosure controls and procedures and   presented in this report our conclusions about the effectiveness of the   disclosure controls and procedures, as of the end of the period covered by   this report based on such evaluation; and |
|   |                                                                                                                                                                                                                                                                                                                                                                    |   |
|   | d)                                                                                                                                                                                                                                                                                                                                                                      | Disclosed in this   report any change in the issuer’s internal control over financial reporting   that occurred during the period covered by the annual report that has   materially affected, or is reasonably likely to materially affect, the   issuer’s internal control over financial reporting; and |
|   |                                                                                                                                                                                                                                                                                                                                                                    |
| 5.     | The issuer’s other   certifying officer(s) and I have disclosed, based on our most recent   evaluation of internal control over financial reporting, to the issuer’s   auditors and the audit committee of the issuer’s board of directors (or   persons performing the equivalent functions):                                                      |
|   |                                                                                                                                                                                                                                                                                                                                                                    |
|   | a)                                                                                                                                                                                                                                                                                                                                                                      | All significant   deficiencies and material weaknesses in the design or operation of internal   control over financial reporting which are reasonably likely to adversely   affect the issuer’s ability to record, process, summarize and report   financial information; and |
|   |                                                                                                                                                                                                                                                                                                                                                                    |   |
|   | b)                                                                                                                                                                                                                                                                                                                                                                      | Any fraud, whether or   not material, that involves management or other employees who have a   significant role in the issuer’s internal control over financial reporting. |

 

 
| March 3, 2017 |                      |
|--------------------|---------------------------|
|               | /s/ Donald Tremblay       |
|               | Donald   Tremblay         |
|               | Chief   Financial Officer |

 

----